diff --git a/federatedscope/autotune/algos.py b/federatedscope/autotune/algos.py
index 392f5bfcb..c37a885e0 100644
--- a/federatedscope/autotune/algos.py
+++ b/federatedscope/autotune/algos.py
@@ -19,6 +19,21 @@
 logger = logging.getLogger(__name__)
 
 
+def make_trial(trial_cfg):
+    setup_seed(trial_cfg.seed)
+    data, modified_config = get_data(config=trial_cfg.clone())
+    trial_cfg.merge_from_other_cfg(modified_config)
+    trial_cfg.freeze()
+    # TODO: enable client-wise configuration
+    Fed_runner = FedRunner(data=data,
+                           server_class=get_server_cls(trial_cfg),
+                           client_class=get_client_cls(trial_cfg),
+                           config=trial_cfg.clone())
+    results = Fed_runner.run()
+    key1, key2 = trial_cfg.hpo.metric.split('.')
+    return results[key1][key2]
+
+
 class TrialExecutor(threading.Thread):
     """This class is responsible for executing the FL procedure with a given trial configuration in another thread.
     """
@@ -106,46 +121,61 @@ def _setup(self):
         ]
 
     def _evaluate(self, configs):
-        flags = [threading.Event() for _ in range(self._cfg.hpo.num_workers)]
-        for i in range(len(flags)):
-            flags[i].set()
-        threads = [None for _ in range(len(flags))]
-        thread_results = [dict() for _ in range(len(flags))]
-
-        perfs = [None for _ in range(len(configs))]
-        for i, config in enumerate(configs):
-            available_worker = 0
-            while not flags[available_worker].is_set():
-                available_worker = (available_worker + 1) % len(threads)
-            if thread_results[available_worker]:
-                completed_trial_results = thread_results[available_worker]
-                cfg_idx = completed_trial_results['cfg_idx']
-                perfs[cfg_idx] = completed_trial_results['perf']
-                logger.info(
-                    "Evaluate the {}-th config {} and get performance {}".
-                    format(cfg_idx, configs[cfg_idx], perfs[cfg_idx]))
-                thread_results[available_worker].clear()
-
-            trial_cfg = self._cfg.clone()
-            trial_cfg.merge_from_list(config2cmdargs(config))
-            flags[available_worker].clear()
-            trial = TrialExecutor(i, flags[available_worker],
-                                  thread_results[available_worker], trial_cfg)
-            trial.start()
-            threads[available_worker] = trial
-
-        for i in range(len(flags)):
-            if not flags[i].is_set():
-                threads[i].join()
-        for i in range(len(thread_results)):
-            if thread_results[i]:
-                completed_trial_results = thread_results[i]
-                cfg_idx = completed_trial_results['cfg_idx']
-                perfs[cfg_idx] = completed_trial_results['perf']
+        if self._cfg.hpo.num_workers:
+            # execute FL in parallel by multi-threading
+            flags = [
+                threading.Event() for _ in range(self._cfg.hpo.num_workers)
+            ]
+            for i in range(len(flags)):
+                flags[i].set()
+            threads = [None for _ in range(len(flags))]
+            thread_results = [dict() for _ in range(len(flags))]
+
+            perfs = [None for _ in range(len(configs))]
+            for i, config in enumerate(configs):
+                available_worker = 0
+                while not flags[available_worker].is_set():
+                    available_worker = (available_worker + 1) % len(threads)
+                if thread_results[available_worker]:
+                    completed_trial_results = thread_results[available_worker]
+                    cfg_idx = completed_trial_results['cfg_idx']
+                    perfs[cfg_idx] = completed_trial_results['perf']
+                    logger.info(
+                        "Evaluate the {}-th config {} and get performance {}".
+                        format(cfg_idx, configs[cfg_idx], perfs[cfg_idx]))
+                    thread_results[available_worker].clear()
+
+                trial_cfg = self._cfg.clone()
+                trial_cfg.merge_from_list(config2cmdargs(config))
+                flags[available_worker].clear()
+                trial = TrialExecutor(i, flags[available_worker],
+                                      thread_results[available_worker],
+                                      trial_cfg)
+                trial.start()
+                threads[available_worker] = trial
+
+            for i in range(len(flags)):
+                if not flags[i].is_set():
+                    threads[i].join()
+            for i in range(len(thread_results)):
+                if thread_results[i]:
+                    completed_trial_results = thread_results[i]
+                    cfg_idx = completed_trial_results['cfg_idx']
+                    perfs[cfg_idx] = completed_trial_results['perf']
+                    logger.info(
+                        "Evaluate the {}-th config {} and get performance {}".
+                        format(cfg_idx, configs[cfg_idx], perfs[cfg_idx]))
+                    thread_results[i].clear()
+
+        else:
+            perfs = [None] * len(configs)
+            for i, config in enumerate(configs):
+                trial_cfg = self._cfg.clone()
+                trial_cfg.merge_from_list(config2cmdargs(config))
+                perfs[i] = make_trial(trial_cfg)
                 logger.info(
                     "Evaluate the {}-th config {} and get performance {}".
-                    format(cfg_idx, configs[cfg_idx], perfs[cfg_idx]))
-                thread_results[i].clear()
+                    format(i, config, perfs[i]))
 
         return perfs
 
diff --git a/federatedscope/core/configs/cfg_hpo.py b/federatedscope/core/configs/cfg_hpo.py
index a54bf0298..dae42b6e3 100644
--- a/federatedscope/core/configs/cfg_hpo.py
+++ b/federatedscope/core/configs/cfg_hpo.py
@@ -10,7 +10,7 @@ def extend_hpo_cfg(cfg):
     cfg.hpo = CN()
     cfg.hpo.working_folder = 'hpo'
     cfg.hpo.ss = ''
-    cfg.hpo.num_workers = 1
+    cfg.hpo.num_workers = 0
     #cfg.hpo.init_strategy = 'random'
     cfg.hpo.init_cand_num = 16
     cfg.hpo.log_scale = False
@@ -56,6 +56,8 @@ def assert_hpo_cfg(cfg):
     assert cfg.hpo.scheduler in ['rs', 'sha',
                                  'pbt'], "No HPO scheduler named {}".format(
                                      cfg.hpo.scheduler)
+    assert cfg.hpo.num_workers >= 0, "#worker should be non-negative but given {}".format(
+        cfg.hpo.num_workers)
     assert len(cfg.hpo.sha.budgets) == 0 or len(
         cfg.hpo.sha.budgets
     ) == cfg.hpo.sha.elim_round_num, \