Abstract: An analytic approach to all-optical switch was present, and the two-photon absorption effect were taking into account to analyze all-optical switch, which is based on two-dimensional photonic crystal directional coupler, by means of the finite-difference time-domain method. The numerical study shows that, for short device and high intensity control beam, nonlinear two-photon absorption(TPA) can take effect on the process of coupling action in all-optical switch, and then change the transmission characteristics of input beam. Therefore, under realistic conditions, TPA should be considered in desgning all-optical switch devices based on photonic crystal directional coupler.