If you want to study in political science, your language skill (English) must be very good - not only good at taking test, but also good at debating in English and writing with persuasion power.

　　A simple test of writing is to write an application essay and then mail it to the Chinese students in those Ivy League schools. Ask them to check with American professors or admission staff. If they think it is good, then you may have a chance.

　　At last, you need to find a way to express your compelling reason for a major study change. The Ivy League schools take students' characters seriously. Be prepared to present yourself in the most positive way.

　　Hope this helps.