when i click add button,t want to create new text field

see this script
Dynamically textbox

Try this,

<div id="div2"></div> 

<input type="button" id="btnok" onclick="addText();" value="text" />
        <br /> 

<script type="text/javascript">
function addText()
        {
        var div1=document.getElementById("div2");
        div1.innerHTML="<input type='text'/>";
        }
 </script>

try below code:
Method1:
call at button click event server side:

lblCessCategory.Text = CessDetail + " ";
lblCessCategory.Text = lblCessCategory.Text + ds.Tables[0].Rows[i]["CessCategoryName"].ToString();

lblCessCategory.Text = lblCessCategory.Text + "";
lblCessCategory.Text = lblCessCategory.Text + "<input type='button' id='btnID'>";

lblCessCategory.Text = lblCessCategory.Text + "";

lblCessCategory.Text = lblCessCategory.Text + "<input type='text' id='txtID'>";
lblCessCategory.Text = lblCessCategory.Text + " ";


put one label at .aspx page. Label id will be lblCessCategory .

Method2:

You can call javascript function for doing this as told in last solution by shobhna.