The lateral periodic porosity structure on porous silicon(PS) layer was obtained by photo-dissolution process by using two coherent laser beams falling on the surface of sample to form the interfering pattern on porous silicon in HF solution.The oxidized PS grating coupler was fabricated firstly in our experiment.The coupling between the radiating mode and guided mode was realized successfully.The effective refractive index was determined by measuring the direction of the input beam or output diffracted beam.