diff --git a/expression/util.go b/expression/util.go
index a6d9ef0d6169d..7929d3384c78f 100644
--- a/expression/util.go
+++ b/expression/util.go
@@ -538,6 +538,41 @@ func PushDownNot(ctx sessionctx.Context, expr Expression) Expression {
 	return newExpr
 }
 
+// ContainOuterNot checks if there is an outer `not`.
+func ContainOuterNot(expr Expression) bool {
+	return containOuterNot(expr, false)
+}
+
+// containOuterNot checks if there is an outer `not`.
+// Input `not` means whether there is `not` outside `expr`
+//
+// eg.
+//    not(0+(t.a == 1 and t.b == 2)) returns true
+//    not(t.a) and not(t.b) returns false
+func containOuterNot(expr Expression, not bool) bool {
+	if f, ok := expr.(*ScalarFunction); ok {
+		switch f.FuncName.L {
+		case ast.UnaryNot:
+			return containOuterNot(f.GetArgs()[0], true)
+		case ast.IsTruthWithNull, ast.IsNull:
+			return containOuterNot(f.GetArgs()[0], not)
+		default:
+			if not {
+				return true
+			}
+			hasNot := false
+			for _, expr := range f.GetArgs() {
+				hasNot = hasNot || containOuterNot(expr, not)
+				if hasNot {
+					return hasNot
+				}
+			}
+			return hasNot
+		}
+	}
+	return false
+}
+
 // Contains tests if `exprs` contains `e`.
 func Contains(exprs []Expression, e Expression) bool {
 	for _, expr := range exprs {
diff --git a/planner/core/integration_test.go b/planner/core/integration_test.go
index 847af9161c092..2e2076d55fa93 100644
--- a/planner/core/integration_test.go
+++ b/planner/core/integration_test.go
@@ -5150,3 +5150,29 @@ func (s *testIntegrationSuite) TestIndexMergeWithCorrelatedColumns(c *C) {
 	}
 
 }
+
+func (s *testIntegrationSuite) TestIssue20510(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+
+	tk.MustExec("drop table if exists t1, t2")
+	tk.MustExec("CREATE TABLE t1 (a int PRIMARY KEY, b int)")
+	tk.MustExec("CREATE TABLE t2 (a int PRIMARY KEY, b int)")
+	tk.MustExec("INSERT INTO t1 VALUES (1,1), (2,1), (3,1), (4,2)")
+	tk.MustExec("INSERT INTO t2 VALUES (1,2), (2,2)")
+
+	tk.MustQuery("explain format=brief SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.a WHERE not(0+(t1.a=30 and t2.b=1));").Check(testkit.Rows(
+		"Selection 8000.00 root  not(plus(0, and(eq(test.t1.a, 30), eq(test.t2.b, 1))))",
+		"└─MergeJoin 10000.00 root  left outer join, left key:test.t1.a, right key:test.t2.a",
+		"  ├─TableReader(Build) 8000.00 root  data:Selection",
+		"  │ └─Selection 8000.00 cop[tikv]  not(istrue_with_null(plus(0, and(eq(test.t2.a, 30), eq(test.t2.b, 1)))))",
+		"  │   └─TableFullScan 10000.00 cop[tikv] table:t2 keep order:true, stats:pseudo",
+		"  └─TableReader(Probe) 10000.00 root  data:TableFullScan",
+		"    └─TableFullScan 10000.00 cop[tikv] table:t1 keep order:true, stats:pseudo"))
+	tk.MustQuery("SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.a WHERE not(0+(t1.a=30 and t2.b=1));").Check(testkit.Rows(
+		"1 1 1 2",
+		"2 1 2 2",
+		"3 1 <nil> <nil>",
+		"4 2 <nil> <nil>",
+	))
+}
diff --git a/planner/core/rule_predicate_push_down.go b/planner/core/rule_predicate_push_down.go
index feed34d7ee567..2d90c647933e1 100644
--- a/planner/core/rule_predicate_push_down.go
+++ b/planner/core/rule_predicate_push_down.go
@@ -376,6 +376,9 @@ func simplifyOuterJoin(p *LogicalJoin, predicates []expression.Expression) {
 // If it is a disjunction of null-rejected conditions.
 func isNullRejected(ctx sessionctx.Context, schema *expression.Schema, expr expression.Expression) bool {
 	expr = expression.PushDownNot(ctx, expr)
+	if expression.ContainOuterNot(expr) {
+		return false
+	}
 	sc := ctx.GetSessionVars().StmtCtx
 	sc.InNullRejectCheck = true
 	result := expression.EvaluateExprWithNull(ctx, schema, expr)
diff --git a/planner/core/testdata/plan_suite_unexported_in.json b/planner/core/testdata/plan_suite_unexported_in.json
index f32d4d4ab8123..06c90571e11fe 100644
--- a/planner/core/testdata/plan_suite_unexported_in.json
+++ b/planner/core/testdata/plan_suite_unexported_in.json
@@ -556,7 +556,9 @@
       "select * from t t1 left join t t2 on t1.b = t2.b where not (t1.c > 1 or t2.c > 1);",
       "select * from t t1 left join t t2 on t1.b = t2.b where not (t1.c > 1 and t2.c > 1);",
       "select * from t t1 left join t t2 on t1.b > 1 where t1.c = t2.c;",
-      "select * from t t1 left join t t2 on true where t1.b <=> t2.b;"
+      "select * from t t1 left join t t2 on true where t1.b <=> t2.b;",
+      "select * from t t1 left join t t2 on t1.b = t2.b where not(0+(t1.c=1 and t2.c=2));",
+      "select * from t t1 left join t t2 on t1.b = t2.b where not(t1.c) and not(t2.c)"
     ]
   },
   {
diff --git a/planner/core/testdata/plan_suite_unexported_out.json b/planner/core/testdata/plan_suite_unexported_out.json
index 391797fa59644..4fc39a9e7d4d0 100644
--- a/planner/core/testdata/plan_suite_unexported_out.json
+++ b/planner/core/testdata/plan_suite_unexported_out.json
@@ -991,6 +991,14 @@
       {
         "Best": "Join{DataScan(t1)->DataScan(t2)}->Sel([nulleq(test.t.b, test.t.b)])->Projection",
         "JoinType": "left outer join"
+      },
+      {
+        "Best": "Join{DataScan(t1)->DataScan(t2)}(test.t.b,test.t.b)->Sel([not(plus(0, and(eq(test.t.c, 1), eq(test.t.c, 2))))])->Projection",
+        "JoinType": "left outer join"
+      },
+      {
+        "Best": "Join{DataScan(t1)->DataScan(t2)}(test.t.b,test.t.b)->Projection",
+        "JoinType": "inner join"
       }
     ]
   },