A three-dimensional finite-difference time-domain (FDTD) method is applied to analyze the performance of a dual-polarized wideband patch antenna in this paper. The simulated results obtained by the FDTD method are compared with measured data. And effects of different design parameters, including inner and outer radiuses of annular-ring slot, cross-slot width, and feed-line length, on the antenna performance are studied. Furthermore, the time-domain field distribution is presented in this paper.