输入框只能包括中文、英文字母、数字和下划线或者空格

 <input id="txtInput" type="text" />

<input id="Button1" type="button" value="button"  onclick="javascript:inputWord()" />

js

 <script language="javascript" type="text/javascript">
        function inputWord() {
            var vRtxtUserName = document.getElementById("txtInput").value;
            var reg = /s{2,}/g;
            vRtxtUserName = vRtxtUserName.replace(reg, " ");//将多空格过滤
            if (!/^[a-zA-Z0-9_u4e00-u9fa5" "]+$/.test(vRtxtUserName)) {
                alert("输入框只能包括中文、英文字母、数字和下划线或者空格！");
                window.location.href = "index.html";
               
            }
            window.location.href = "/xxxx.aspx?input="+encodeURIComponent(vRtxtUserName);
        }
    </script>

cs

 protected void Page_Load(object sender, EventArgs e)
 {
            bool bolInput = IsValidChineseEnglishSpace(HttpUtility.UrlDecode(Request.QueryString["input"]));

}
  public  bool IsValidChineseEnglishSpace(string input)
        {
            return Regex.IsMatch(input, @"^[a-zA-Z0-9_u4e00-u9fa5" "]+$");
        }

//去除的办法

/// <summary>
    /// 替换字符中文、字母、数字以外的字符替换成空。
    /// </summary>
    /// <param name="asString"></param>
    /// <returns></returns>
    public static string TrimCharacter(string asString)
    {
        string sResult = "";
        string sCharacterRegx = "[^a-zA-Z0-9u4E00-u9FFF]";
        Regex rgVal = new Regex(sCharacterRegx);
        sResult = rgVal.Replace(asString, "");
        return sResult;
    }