string input = @"\\x00\\x00\\x00\\x00\\xaa\\x8f\\x63\\x3b";
System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex(
    @"\\(\\x[0-9a-f]{2})",
    System.Text.RegularExpressions.RegexOptions.IgnoreCase
);
string output = reg.Replace(input,"$1");

------解决方案--------------------

C# code
            string s = @"\\x00\\x00\\x00\\x00\\xaa\\x8f\\x63\\x3b";
            string r = s.Replace(@"\\x", @"\x");
            Console.Write(r);
            Console.ReadKey();