remove all of the value in the web form

Similar to how I answered your other question, loop over the appropriate container's Controls collection, but do so using a for loop, and just call the RemoveAt method.

e.g.

for (int i = form.Controls.Count - 1; i >= 0; i--)
{
    form.Controls.RemoveAt(i);
}

Select all Open in new window

I think the OP wants to know how to remove all the controls' values, not remove the controls themselves.

If that be the case:

foreach (Control formControl in this.Form.Controls)
{
    TextBox txt = formControl as TextBox;

    if (txt != null)
    {
        txt.Text = string.Empty;
        continue;
    }

    DropDownList ddl = formControl as DropDownList;

    if (ddl != null)
    {
        ddl.SelectedIndex = -1;
        continue;
    }

    RadioButton radio = formControl as RadioButton;

    if (radio != null)
    {
        radio.Checked = false;
        continue;
    }

    CheckBox check = formControl as CheckBox;

    if (check != null)
    {
        check.Checked = false;
        continue;
    }
}

Select all Open in new window

In which code-behind method (or more correctly, which event handler) are you attempting to use this code?