function CheckForm() {
    if (document.getElementById('txtUsername').value == "") {
        alert("请输入用户名！");
        document.getElementById('txtUsername').focus();
        return false;
    }
    if (document.getElementById('txtPassword').value == "") {
        alert("请输入密码！");
        document.getElementById('txtPassword').focus();
        return false;
    }
    return true;
}