I made changes in my javascript
<script type="text/javascript">
function prd_download(ele)
{
var selected_images = $(".img_check:checked");
var job_no = $("#product_table").attr("jobno");
var image_name = new Array();
for(i = 0; i < selected_images.length; i++)
{
image_name[i] = $(selected_images[i]).attr('image');
}
window.location.href = "<?php echo site_url('project_controller/file_download') ?>?file_name="+ image_name +"&jobno="+ job_no;
}
</script>
In javascript I called controller directly, cause $.get
function treat like call back...
Now its working fine...! :) :D