function CheckThisForm()
{
var thisForm = document.forms[0];
var j = 0;
for(i=0;i<thisForm.length;i++)
{
if(thisForm.elements[i].name.indexOf("CheckBox")!=-1)
{
if (thisForm.elements[i].checked)
{
j++;
}
}
}
alert(j);
}
<form id="form1" runat="server">
<asp:CheckBox ID="CheckBox1" runat="server" />
<asp:CheckBox ID="CheckBox2" runat="server" />
<asp:CheckBox ID="CheckBox3" runat="server" />
<input id="Button1" type="button" value="button" onclick="CheckThisForm()" />
</form>
不过要保证这些checkbox的id要有一定的规律,可以试一下