Thanks for all advice. Just as what Hjort said, so I think that the GMAT itself is a good opportunity to learn English. Frankly speaking, I plan to retake the test partly because I feel that during the preparation and the formal exam this time my verbal skills should be imporved since I took the GMAT in Jan. 2003.
I just want to make sure that the books and the strategy I used are in the right way to prepare for the GMAT. And what's more important is, I BELIEVE that I can perform better on the basis of my hardworking.
I also want to thanks ashwini17. I have applied for some schools last year and I know that there are other things at least as important as the GMAT score. However, the school that I want to enter did not give me an offer with the score 630 and I think one year more working experience may not enough to convince the admission commitee.