Abstract
In this paper we mainly discuss the theta corrspondence of irreducible cuspidal characters of finite unitary groups. Firstly, we distinguish irreducible unipotent characters of finite unitary groups by Lusztig's discussion. We use the centralizers of semisimple elements of finite unitary groups to know which irreducible characters of finite unitary groups are cuspidal. Then we introduce the induction principle and preservation principle. Finally, we clarify the theta correspondence between unitary groups by the induction principle and preservation principle, especially for U0(q), U1(q), U2(q), and U3(q).