var
    SourceStr,str:string;
    i:integer;
begin
    SourceStr:='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    randomize;
    for i:=1 to 16 do
      str:=str+sourcestr[Random(62)+1];
    ShowMessage(str);
end;

[注：生成长度为16位数，取值范围为'A-Z'a-z''0-9'的随机数]