The invention discloses a two-dimensional photonic crystal logic NOR gate based on the auto-collimation interference effect. The two-dimensional photonic crystal logic NOR gate comprises a square-crystal-lattice photonic crystal, and the photonic crystal has the auto-collimation interference effect; three line defects arranged in the propagation direction of an auto-collimation beam are manufactured inside the photonic crystal to serve as three beam splitters S<1>, S<2> and S<3>, the beam splitter S<1> achieves total reflection, and the beam splitter S<2> and the beam splitter S<3> achieve partial reflection; the distance deltal<1> between the beam splitter S<1> and the beam splitter S<2> is equal to 25a, and the distance deltal<2> between the beam splitter S<2> and the beam splitter S<3> is equal to 15a, wherein a is the lattice constant of the photonic crystal; three incident ports and an output port are formed in the photonic crystal, and the three incident ports include two input beam ports and one reference light port. The phase difference between two input beams is adjusted by adjusting the column radii of the line defects and the light path difference between the two input beams, and the two input beams achieve the logic function through destructive interference or constructive interference. The logic NOR gate has better adaptability.