private char constant =        

{           'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',           'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'         };    

public GenerateRandom( Length)    

{         .Text.StringBuilder Random = .Text.StringBuilder(constant.Length);

Random rd = Random;         for ( i = 0; i < Length; i)        

{             Random.Append(constant[rd.Next(constant.Length-1)]);         }        

Random..ToLower;     }  

:Response.Write(GenerateRandom(5));

如果想返回数字和字母组合话你可以在里自己加上几个数字就行了