Dear Huang:

all MEMS simulation software that I am aware of is very expensive.  The
company I interact with, Microcosm, sells a license for about $100,000.
They do, however, have academic discounts (I don't know exactly how big,
but certainly significant).  They have a package that combines design
and simulation under one shell, which saves you a lot of trouble.  They
can model mechanics, electrostatics and some electrodynamics, fluid
mechanics etc.

If interested, please let me know and I can get more detailed
information for you.

Good luck with your thesis project.

Alex