Hi rakeshkuma,
In latest version of AjaxToolKit Accordion control supports only one active pane at a time.
You can have all panes collapsed stage but only once can be active at a time.
For what you need, you can use multiple collapsible panels or alternative you can be use jquery Accordion.
HTML
<asp:Button Text="Expand all" class="accordion-expand-collapse" runat="server" />
<div id="accordion">
    <h3 class="accordion-header">    1. Accordion</h3>
    <div>
        <p>
            The Accordion is a web control that allows you to provide multiple panes and display them one at a time.
            It is like having several CollapsiblePanels where only one can be expanded at a time. The Accordion is implemented as a web control that contains
        </p>
    </div>
    <h3 class="accordion-header">    2. AutoSize</h3>
    <div>
        <p>It also supports three AutoSize modes so it can fit in a variety of layouts.</p>
    </div>
    <h3 class="accordion-header">    3. Control or Extender</h3>
    <div>
        <p>
            The Accordion is written using an extender like most of the other extenders in the AJAX Control Toolkit.
        </p>
    </div>
</div>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/themes/smoothness/jquery-ui.css" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/jquery-ui.min.js"></script>
<script>
    $(function () {
        $("#accordion").accordion();
        $('.accordion-expand-collapse').on('click', function () {
            $('#accordion .ui-accordion-header:not(.ui-state-active)').next().slideToggle();
            $(this).val($(this).val() == 'Expand all' ? 'Collapse all' : 'Expand all');
            $(this).toggleClass('collapse');
            return false;
        });
    });
</script>