Hi Winnie,
The answer to your question depends on where you want to go to school (rankings, U.S. only or are you considering Europe too, etc), as well as what the other aspects of your application look like (eg. career progression, unique experiences you've had, academic record, leadership experience, etc). Most of the top 20 schools' 80% GMAT score ranges start at 640 on the low end. That said, I had a client this year with a <600 score who got into Columbia and interviewed with several other top programs (waiting on results) because she has a very, very interesting profile outside of her scores. Apologies as there isn't a simple answer here; the GMAT is only one factor. We offer a free consultation if you want to discuss further:
Vantage Point MBA Admissions Consulting.
Good luck!
Vantage Point MBA Admissions Consulting