I am going to study computer science next year. I am afraid I can't handle the mathematics in the university because I only know some basic mathematics, such as set theory, simple probability, simple matrix operation and I don't know calculus.
I'd suggest getting a good handle on Discrete Mathematics, first and foremost, though I'd never discourage anyone from studying calculus and linear algebra, if they desire to do so. Of more immediate use, however, would be studying Discrete Mathematics. Unfortunately, most textbooks in discrete mathematics are somewhat expensive.
One great choice, for a "beginner" (in that it presumes very little in the way of a mathematics background), is Susanna S. Epp's Discrete Mathematics with Applications. This text, however, is very expensive.
Another text which is excellent is Edward R. Scheinerman’s Mathematics: A Discrete Introduction, though it is geared more for math majors than for computer science majors. I think it's less expensive than Epp's text, so I'd suggest taking a look at it, as well.
If cost is an issue, there are some well known notes that are freely accessible and free. For example, see
WWWL Chen, Discrete Mathematics
Marcel B. Finan, Lecture Notes in Discrete Mathematics
László Lovász, Katalin Vesztergombi, Discrete Mathematics
Assorted and freely accessible E-books in Discrete Mathematitics
See also this earlier post, where the question posted sought recommendations for a great text in discrete mathematics. The "leading" answer there recommends Concrete Mathematics by Knuth and company, which is a phenomenal text, but some students may find it difficult to tackle without a more solid foundation in mathematics, including at least some Calculus. But do please do take a look at the text. If you hope to be a computer scientist, Concrete Mathematics will be, either now or later, a "must read" text book. (It is also considerably less expensive than many introductory Discrete Mathematics textbooks!)