diff --git a/zero-framework.el b/zero-framework.el
index 6e2cf992a06931f5f6fd943942cfaf914f05c894..7b6e11bf6f7fc4a50780dbe11221ca4b62b35be8 100644
--- a/zero-framework.el
+++ b/zero-framework.el
@@ -186,7 +186,7 @@ if t, `zero-debug' will output debug msg in *zero-debug* buffer")
     (zero-panel-show-candidates
      (funcall zero-get-preedit-str-for-panel-func)
      (length candidates-on-page) candidates-on-page)
-    (zero-debug "candidates: %s\n  " (s-join "\n  " candidates-on-page))
+    (zero-debug "candidates:\n  %s\n  " (s-join "\n  " candidates-on-page))
     (destructuring-bind (x y) (zero-get-point-position)
       (zero-panel-move x y))))
 
diff --git a/zero-pinyin-service.el b/zero-pinyin-service.el
index ee63b8898c6680898bae90e5511bed7e8533268f..3f5eb27a0116c10d2af1cda50951a22dbdff0b04 100644
--- a/zero-pinyin-service.el
+++ b/zero-pinyin-service.el
@@ -36,17 +36,44 @@
 ;; public API
 ;;============
 
-(defun zero-pinyin-service-get-candidates (preedit-str)
-  "get candidates for pinyin in preedit-str synchronously"
-  (zero-pinyin-service-call "GetCandidates" :string preedit-str))
+(defun zero-pinyin-service-get-candidates (preedit-str fetch-size)
+  "get candidates for pinyin in preedit-str synchronously.
 
-(defun zero-pinyin-service-get-candidates-async (preedit-str get-candidates-complete)
-  "get candidates for pinyin in preedit-str asynchronously"
+preedit-str the preedit-str, should be pure pinyin string
+fetch-size try to fetch this many candidates or more"
+  (zero-pinyin-service-call "GetCandidates" :string preedit-str :uint32 fetch-size))
+
+(defun zero-pinyin-service-get-candidates-async (preedit-str fetch-size get-candidates-complete)
+  "get candidates for pinyin in preedit-str asynchronously.
+
+preedit-str the preedit-str, should be pure pinyin string
+fetch-size try to fetch this many candidates or more"
   (zero-pinyin-service-async-call
-   "GetCandidates" get-candidates-complete :string preedit-str))
+   "GetCandidates" get-candidates-complete :string preedit-str :uint32 fetch-size))
 
-(defun zero-panel-quit ()
+(defun zero-pinyin-service-quit ()
   "quit panel application"
   (zero-pinyin-service-async-call "Quit" nil))
 
-(provide 'zero-panel)
+;;================
+;; some app test
+;;================
+
+(ert-deftest zero-pinyin-service-get-candidates ()
+  (destructuring-bind (cs ls) (zero-pinyin-service-get-candidates "liyifeng" 1)
+    (should (equal (first cs) "李易峰"))
+    (should (= (first ls) 8)))
+  (destructuring-bind (cs ls) (zero-pinyin-service-get-candidates "wenti" 1)
+    (should (equal (first cs) "问题"))
+    (should (= (first ls) 5)))
+  (destructuring-bind (cs ls) (zero-pinyin-service-get-candidates "meiyou" 1)
+    (should (equal (first cs) "没有"))
+    (should (= (first ls) 6)))
+  (destructuring-bind (cs ls) (zero-pinyin-service-get-candidates "shi" 1)
+    (should (equal (first cs) "是"))
+    (should (= (first ls) 3)))
+  (destructuring-bind (cs ls) (zero-pinyin-service-get-candidates "de" 1)
+    (should (equal (first cs) "的"))
+    (should (= (first ls) 2))))
+
+(provide 'zero-pinyin-service)
diff --git a/zero-pinyin.el b/zero-pinyin.el
index 7da9809a196d2a20e3e6359362368674b40193ea..7e3a3b0ee04af450917969290088dc9d683904ec 100644
--- a/zero-pinyin.el
+++ b/zero-pinyin.el
@@ -7,6 +7,7 @@
 
 (require 's)
 (require 'zero-framework)
+(require 'zero-pinyin-service)
 
 ;;===============================
 ;; basic data and emacs facility
@@ -19,6 +20,8 @@
   "accompany `zero-candidates', marks how many preedit-str chars are used for each candidate")
 (defvar zero-pinyin-pending-str "")
 (defvar zero-pinyin-pending-preedit-str "")
+(defvar zero-pinyin-initial-fetch-size 20
+  "how many candidates to fetch for the first call to GetCandidates")
 
 ;;=====================
 ;; key logic functions
@@ -40,7 +43,7 @@
 (defun zero-pinyin-build-candidates (preedit-str)
   (if zero-pinyin--build-candidates-use-test-data
       (zero-pinyin-build-candidates-test preedit-str)
-    (let ((result (zero-pinyin-service-get-candidates preedit-str)))
+    (let ((result (zero-pinyin-service-get-candidates preedit-str zero-pinyin-initial-fetch-size)))
       (setq zero-pinyin-used-preedit-str-lengths (second result))
       (first result))))
 
@@ -49,6 +52,7 @@
   (zero-debug "building candidate list async\n")
   (zero-pinyin-service-get-candidates-async
    preedit-str
+   zero-pinyin-initial-fetch-size
    (lambda (candidates matched_preedit_str_lengths)
      (setq zero-pinyin-used-preedit-str-lengths matched_preedit_str_lengths)
      ;; Note: with dynamic binding, this command result in (void-variable
@@ -73,7 +77,7 @@
   (should-not (zero-pinyin-can-start-sequence ?v)))
 
 (defun zero-pinyin-pending-preedit-str-changed ()
-  (zero-build-candidates-async zero-pinyin-pending-preedit-str))
+  (zero-pinyin-build-candidates-async zero-pinyin-pending-preedit-str 'zero-build-candidates-complete))
 
 (defun zero-pinyin-commit-nth-candidate (n)
   "commit nth candidate and return true if it exists, otherwise, return false"