I also need it's respective fetched id from database in comma separator. Instead the lated value override the previous one. 

I tried to use push operation couldn't.

2. <?php $this->widget('CAutoComplete',
3. array(
4.       //name of the html field that will be generated
5.   'name'=>'user_name[]', 
6.       //replace controller/action with real ids
7.   'url'=>array('Privacy/autoCompleteLookup'), 
8.   'max'=>10, //specifies the max number of items to display
9.       
10.       //specifies the number of chars that must be entered 
11.       //before autocomplete initiates a lookup
12.   'minChars'=>1, 
13.   'delay'=>200, //number of milliseconds before lookup occurs
14.   'matchCase'=>false, //match case when performing a lookup?
15.       
16.       //any additional html attributes that go inside of 
17.       //the input field can be defined here
18.   'htmlOptions'=>array('size'=>'40'), 
19.       
20.   'methodChain'=>".result(function(event,item){\$(\"#allow\").val(item[1]); \$(\"#allow\").prepend($(20));})",
21.   'multiple' => true,
22. ));
23.  ?>
24. <?php echo CHtml::hiddenField('allow'); ?> // its equivalent html form is : <input type="hidden" name="allow" >

jQuery part is in line number 20 and the record's is should be in hidden form line number 24

Thank you for your support.