Andrey_szr,
<html>
<head>
<script>
function addtable(){
var table=document.getElementById('tab1');
var tr21=document.createElement('tr');
var td21=document.createElement('td');
var td22=document.createElement('td');
td21.innerHTML='21';
td22.innerHTML='22';
tr21.appendChild(td21);
tr21.appendChild(td22);
table.appendChild(tr21);
}
</script>
</head>
<body>
<table id="tab1">
<tr><td>11</td><td>12</td></tr>
</table>
<input type="button" value="add" onClick="addtable()">
</body>
</html>