string s = "abc//1abc//2abc//3abc";
string[] toks = Regex.Split(s, "//\\d");

------解决方案--------------------
C# code
 protected void Button1_Click(object sender, EventArgs e)
    {
        string s = @"abc//1abc//2abc//3abc";
        string[] arry = System.Text.RegularExpressions.Regex.Split(s, @"//\d");
        
        for (int i = 0; i < arry.Length; i++)
        {
            Response.Write(arry[i]+"</br>");
        }
    }

------解决方案--------------------
2楼的//\\d和这里的@“//\d”是同一个意思。只是多用了一个转义字符。而@本身就具有转义的功能。