The principle of finite difference time domain(FDTD)was presented，A TiO 2 photonic crystal(PC)with(AB) M A structure was designed，in the structure A is TiO 2 ，B is MgF 2 and M=8，and analysis of electromagnetic field in1D photonic scrystal(PC)was performed.The results show that without the doping method，it can also introduce the defect state into the photonic band gap only by changing the structural parame-ter，and the central wavelength and width of the defect state change with the structural parameter.