Abstract: In order to implement the complete band gap of 2-D photonic crystal, the authors adopt the complex unit cell of different structure to construct a kind of photonic crystals, take the method of multiscattering to calculate respectively the different volume fraction and intemal parameter as well as，when the incident light is in different direction， the transmission spectrum of s and p polarizing waves. It is theoretically demonstrated that in the photonic crystal of this kind complex unit cells， as long as the appropriate intermal parameter and volume fraction are selected, the effect of 3-D photonic crystal in 2-D complex photonic crystal can be achieved, i.e. ，the complete band gap can be implemented.