>thank you Terry. I tested this ,but it didn't work. when I set the field format in field property dialog ,set the format to numeric ,and check the negtiv option, the value display always like (322.000)、(23.0000)、（333.000）,could give me some advice on how to make it always two decimal.like (3333.00) 、（33.00)、 （33333.00). thank you.

Well, Michale, actually, what I've done (recently, and it works) is create a character report variable, in which I've stored the expression as I gave it to you, and used the char var in the report, rather than the numeric one. Maybe that's how it works for me (and why I actually DID this :-) - I think I was having the same problem.