diff --git a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/traversers/NeighborRankAPI.java b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/traversers/NeighborRankAPI.java
index a5754fe4ef..3ad6bc58f1 100644
--- a/hugegraph-api/src/main/java/com/baidu/hugegraph/api/traversers/NeighborRankAPI.java
+++ b/hugegraph-api/src/main/java/com/baidu/hugegraph/api/traversers/NeighborRankAPI.java
@@ -67,7 +67,7 @@ public String neighborRank(@Context GraphManager manager,
                                "The source of rank request can't be null");
         E.checkArgument(request.steps != null && !request.steps.isEmpty(),
                         "The steps of rank request can't be empty");
-        E.checkArgument(request.steps.size() <= Long.valueOf(DEFAULT_MAX_DEPTH),
+        E.checkArgument(request.steps.size() <= Long.parseLong(DEFAULT_MAX_DEPTH),
                         "The steps length of rank request can't exceed %s",
                         DEFAULT_MAX_DEPTH);
         E.checkArgument(request.alpha > 0 && request.alpha <= 1.0,
@@ -107,7 +107,7 @@ private static class RankRequest {
         @JsonProperty("alpha")
         private double alpha;
         @JsonProperty("capacity")
-        public long capacity = Long.valueOf(DEFAULT_CAPACITY);
+        public long capacity = Long.parseLong(DEFAULT_CAPACITY);
 
         @Override
         public String toString() {
@@ -124,11 +124,11 @@ private static class Step {
         @JsonProperty("labels")
         public List<String> labels;
         @JsonProperty("degree")
-        public long degree = Long.valueOf(DEFAULT_DEGREE);
+        public long degree = Long.parseLong(DEFAULT_DEGREE);
         @JsonProperty("skip_degree")
         public long skipDegree = 0L;
         @JsonProperty("top")
-        public int top = Integer.valueOf(DEFAULT_PATHS_LIMIT);
+        public int top = Integer.parseInt(DEFAULT_PATHS_LIMIT);
 
         public static final int DEFAULT_CAPACITY_PER_LAYER = 100000;
 
diff --git a/hugegraph-core/src/main/java/com/baidu/hugegraph/traversal/algorithm/NeighborRankTraverser.java b/hugegraph-core/src/main/java/com/baidu/hugegraph/traversal/algorithm/NeighborRankTraverser.java
index 2203064bf4..9e0c59248f 100644
--- a/hugegraph-core/src/main/java/com/baidu/hugegraph/traversal/algorithm/NeighborRankTraverser.java
+++ b/hugegraph-core/src/main/java/com/baidu/hugegraph/traversal/algorithm/NeighborRankTraverser.java
@@ -244,7 +244,9 @@ public Step(HugeGraph g, Directions direction, List<String> labels,
                     long degree, long skipDegree, int top, int capacity) {
             E.checkArgument(top > 0 && top <= MAX_TOP,
                             "The top of each layer can't exceed %s", MAX_TOP);
-
+            E.checkArgument(capacity > 0,
+                            "The capacity of each layer must be > 0, " +
+                            "but got %s", capacity);
             this.edgeStep = new EdgeStep(g, direction, labels, null,
                                          degree, skipDegree);
             this.top = top;