Abstract: The quality factor Q and transmission T of two-dimensional photonic crystal microcavities,which consist of square arrays of Al₂O₃ rods with 5 lattice defects,were simulated by the multiple-scattering computation method.The simulation results show that the quality factor Q and the transmission T are greatly affected by the numbers of dielectric rods L_x,L_y and the radius of dielectric rods.Two-dimensional mircrocavities with high Q and large T are realized through optimizing the structure parameters.In this simulation case, when L_x=13, L_y=17, and r=0.25, the quality factor and the transmission are optimized as 49270 and 91%, respectively.