A PhC all-optical multistep-delay self-OR-transformation logic gate including an optical switch unit, a PhC structure unit, a reference-light, a memory or delayer, a D-type flip-flop unit and a wave absorbing load; a logic signal X is connected to the input port of a two-branch waveguide whose two output ports are respectively connected with the input port of the memory and the logic-signal input port of the optical switch unit; the output port of the memory is connected with the delay-signal input port of the optical switch unit; the reference-light source is connected with the reference-light input port of the optical switch unit whose three intermediate-signal output ports are respectively connected with the first and second intermediate-signal input ports of the PhC structure unit and the wave absorbing load; and the output port of the PhC structure unit is connected with the D-signal input port of the D-type flip-flop unit.