An all-optical diode structure based on Fano micro-cavity at the side of 2D photonic crystal waveguide is designed to realize the nonreciprocal transmission of light. The key technique is to break the spatial symmetry of Fano micro-cavity structure by using a simple reflecting layer in the photonic crystal (PC) waveguide, so that the coupling efficiency of waveguide on both sides of the reflective layer and micro-cavity is asymmetric. Since the thresholds of incident light intensity required for the nonlinear Kerr material to excite the micro-cavity on both sides of the waveguide are different, the function of one-way conduction is achieved. The transmission properties and performance are numerically simulated and investigated by finite-difference time-domain (FDTD) method. The results show that forward transmission and backward cut-off all-optical diode effect can be achieved in this structure with low light intensity threshold. The structure has ultra-fast response time, which can reach the order of picoseconds. It also has high maximum transmittance (about 90%), and high positive and negative transmittance. The design based on photonic crystal structure enables the device to have good work wavelength tunable characteristics, which makes it easy to produce and integrate with other devices on the basis of current semiconductor technology.