Based on the general form of Fresnel diffraction,light intensity distribution in laser interference crystallization with a phase shifting grating mask (PSGM) was calculated.Two-dimensional (2D) periodic nanocrystalline silicon (nc-Si) array was fabricated by laser interference crystallization combined with 2D-PSGM.The light intensity irradiated on the surface of a-Si:H samples can be modulated by the PSGM with the periodicity of 400 nm.Experimental results demonstrate that the periodicity of 2D nc-Si array is the same as that of the PSGM,the crystalline regions of nc-Si array are consistant with the simulated results.