Provided is a two-dimensional photonic crystal logic equivalence gate based on an auto-collimation interference effect. The two-dimensional photonic crystal logic equivalence gate comprises a tetragonal lattice photonic crystal which has the auto-collimation interference effect; three line defects serving as three beam splitters S1, S2 and S3 are made inside the photonic crystal and arranged in the auto-collimation beam propagation direction; the distance between the beam splitter S1 and the beam splitter S2 is delta l1=12a, and the distance between the beam splitter S2 and the beam splitter S3 is delta l2=25a, wherein a is a lattice constant of the photonic crystal; the photonic crystal is internally provided with three incident ports and one output port, and the three incident ports are two input beam ports and one reference light port. The phase difference between two input beams is adjusted by adjusting the defect column radius and the light path difference between the two input beams, and the two input beams achieve the logical function through destructive interference or destructive interference. The logic equivalence gate is not limited by physical boundaries in traditional waveguide and has better adaptability.