////////////////////////////

string inputstr = "@{AbcD},@{bbbb},@{ABcd}";

string pmType = "@";

string regTxt = (pmType + "s*{s*" + "abcd" + "s*}").Replace("(", "(").Replace(")", ")");

//string regTxt = (pmType + "s*{s*" + "aaaa" + "s*}").Replace("(", "(").Replace(")", ")");

// string regTxt = @"@s*{s*aaaas*}";

// string regTxt = @"@s*{s*aaaas*}/gi";

inputstr = Regex.Replace(inputstr, regTxt, "CCC", RegexOptions.IgnoreCase | RegexOptions.Compiled);

///////////////

对于小文本不使用 RegexOptions.Compiled；