Discontinuous Galerkin Time Domain (DGTD) method appears to be very promising which combines the advantages of unstructured mesh in Finite Element Time Domain (FETD) and explicit scheme in Finite Difference Time Domain (FDTD). This paper first describes principle of DGTD base on vector basis function. Secondly, Specific method for incident plane wave is given for scattering problem. At last, the monostatic Radar Cross Section (RCS) of PEC sphere, medium sphere and the PEC bullet are computed by DGTD method. The numerical results illustrate the feasibility and correctness of the presented scheme. The study of this paper is a foundation for analyzing the RCS of complex target.