Hi Chunilangl,

You can follow below approach. 

1. configure an Edit validate rule for the Property 

2. Inside the Editvalidate rule enter below code - In my case I am populating the autocomplete data from a data page D_testdatalist. and checking against the "Name" values which is inside the list page. 

ClipboardPage d_page = tools.findPage("D_TestDataList");
String enteredval = theValue;
ClipboardProperty resultList = d_page.getProperty("pxResults");
int flag = 0;
for(int i=1;i<resultList.size();i++){
    ClipboardProperty d_pageFields = d_page.getProperty("pxResults("+i+")");
    ClipboardPage page = d_pageFields.getPageValue();
    String userDefName = page.getString("Name");
    if(enteredval.equals(userDefName)){
        flag=1;
        break;
    }
}
if(flag==1){
  return true;
}
else{
   theProperty.addMessage("Incorrect value choosen for autocomplete");
	 return false;
}

3. Configure a Refresh section Onchange of the autocomplete. 

You will get the Desired result. 

Hope, this will solve your problem. If you find it helpful. Please mark my answer as correct || helpful. 

Incase if you face any issue please drop a note.