diff --git a/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller.go b/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller.go
index b461eed7c..856462305 100644
--- a/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller.go
+++ b/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller.go
@@ -3,6 +3,7 @@ package klusterletcontroller
 import (
 	"context"
 	"fmt"
+	"sort"
 	"strings"
 	"time"
 
@@ -58,6 +59,19 @@ var operatorOnlyFeatureGates = map[featuregate.Feature]bool{
 	NetworkPolicies: true,
 }
 
+// buildClusterAnnotationsString renders the ClusterAnnotations map into the
+// comma-separated "key1=value1,key2=value2" form consumed by the registration
+// agent's --cluster-annotations flag. Keys are sorted deterministically.
+func buildClusterAnnotationsString(annotations map[string]string) string {
+	filtered := commonhelpers.FilterClusterAnnotations(annotations)
+	arr := make([]string, 0, len(filtered))
+	for k, v := range filtered {
+		arr = append(arr, fmt.Sprintf("%s=%s", k, v))
+	}
+	sort.Strings(arr)
+	return strings.Join(arr, ",")
+}
+
 func filterOperatorFeatureGates(features []operatorapiv1.FeatureGate) []operatorapiv1.FeatureGate {
 	var filtered []operatorapiv1.FeatureGate
 	for _, f := range features {
@@ -422,12 +436,7 @@ func (n *klusterletController) sync(ctx context.Context, controllerContext facto
 				klusterlet.Spec.RegistrationConfiguration.ClusterClaimConfiguration.ReservedClusterClaimSuffixes, ",")
 		}
 
-		// construct cluster annotations string, the final format is "key1=value1,key2=value2"
-		var annotationsArray []string
-		for k, v := range commonhelpers.FilterClusterAnnotations(klusterlet.Spec.RegistrationConfiguration.ClusterAnnotations) {
-			annotationsArray = append(annotationsArray, fmt.Sprintf("%s=%s", k, v))
-		}
-		config.ClusterAnnotationsString = strings.Join(annotationsArray, ",")
+		config.ClusterAnnotationsString = buildClusterAnnotationsString(klusterlet.Spec.RegistrationConfiguration.ClusterAnnotations)
 
 		// Set AddOnKubeClientRegistrationAuth from the Klusterlet spec
 		if klusterlet.Spec.RegistrationConfiguration.AddOnKubeClientRegistrationDriver != nil &&
diff --git a/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller_test.go b/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller_test.go
index 8dd730f90..f01226766 100644
--- a/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller_test.go
+++ b/pkg/operator/operators/klusterlet/controllers/klusterletcontroller/klusterlet_controller_test.go
@@ -1917,3 +1917,70 @@ func TestCleanWithMultipleKlusterletAgentNamespaces(t *testing.T) {
 		})
 	}
 }
+
+// TestBuildClusterAnnotationsString verifies that the annotations flag string has consistent ordering across multiple runs.
+func TestBuildClusterAnnotationsString(t *testing.T) {
+	const prefix = "agent.open-cluster-management.io"
+	tests := []struct {
+		name        string
+		annotations map[string]string
+		want        string
+	}{
+		{
+			name:        "nil map",
+			annotations: nil,
+			want:        "",
+		},
+		{
+			name:        "empty map",
+			annotations: map[string]string{},
+			want:        "",
+		},
+		{
+			name:        "single key",
+			annotations: map[string]string{prefix + "/foo": "bar"},
+			want:        prefix + "/foo=bar",
+		},
+		{
+			name: "keys sorted lexicographically",
+			annotations: map[string]string{
+				prefix + "/c": "3",
+				prefix + "/a": "1",
+				prefix + "/b": "2",
+			},
+			want: prefix + "/a=1," + prefix + "/b=2," + prefix + "/c=3",
+		},
+		{
+			name: "non-prefixed keys are filtered out",
+			annotations: map[string]string{
+				prefix + "/keep":     "yes",
+				"other.example/drop": "no",
+			},
+			want: prefix + "/keep=yes",
+		},
+		{
+			name: "many keys stable across many invocations",
+			annotations: map[string]string{
+				prefix + "/a": "1",
+				prefix + "/b": "2",
+				prefix + "/c": "3",
+				prefix + "/d": "4",
+				prefix + "/e": "5",
+				prefix + "/f": "6",
+			},
+			want: prefix + "/a=1," + prefix + "/b=2," + prefix + "/c=3," + prefix + "/d=4," + prefix + "/e=5," + prefix + "/f=6",
+		},
+	}
+
+	const iterations = 1000
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			for i := range iterations {
+				got := buildClusterAnnotationsString(tt.annotations)
+				if got != tt.want {
+					t.Fatalf("iteration %d: got %q, want %q (non-deterministic output regresses cluster-annotations flag)", i, got, tt.want)
+				}
+			}
+		})
+	}
+}