string s = "UserName:zhangsan#UserPwd:test#ID:1#Address:湖南";
    protected void Page_Load(object sender, EventArgs e)
    {
        Response.Write(ABC("Address"));
    }

    private string ABC(string srcStr)
    {
        return Regex.Match(s, string.Format(@"(?i)(?:^|#){0}:([^#]+)", srcStr)).Groups[1].Value;
    }

------解决方案--------------------

C# code

 private static string ReturnValue(string srcStr)
        {
            var html = @"UserName:zhangsan#UserPwd:test#ID:1#Address:湖南";
            return Regex.Match(html, @"(?i)([^:#]*)" + srcStr + ":([^:#]*)").Groups[2].Value;
        }
        static void Main(string[] args)
        {
            Console.WriteLine(ReturnValue("UserName"));
            Console.WriteLine(ReturnValue("UserPwd"));
            Console.WriteLine(ReturnValue("ID"));
            Console.WriteLine(ReturnValue("Address"));
        }