The photonic properties of a two-dimensional complex photonic crystal (PC) of square lattice were calculated by finite different time domain (FDTD) method. The photonic band structure, photonic density of states, the transmission and reflection coefficients along ГX direction were obtained. The results indicate a clear correspondence between the photonic band structure and the transmission spectra along ГX direction. The photonic band structure was also shown by the photonic density of states. Furthermore, the theoretical explanation for the opening of the band gap was given.