Using photonic bandgap of photonic crystals (PC) and the grating diffraction effect can improve the efficiency of the light from the light emitling diode (LED),it can expand the application scope of the LED. PC with square lattice of cylindrical unit cells are fabricated in GaN layer of GaN-based blue LED,the light extraction efficiency of GaN-based blue LED influenced by random perturbation of structural parameters are studied by finite-difference time-domain method and its mechanism is analyzed by the bang gap theory.