According to the requirement of the optical communication devices, sub-wavelength grating polarizer was studied based on rigorous coupled-wave analysis (RCWA) and designed with SOI materials. The paper analyzes the grating parameters such as the period, depth, fill groove that influence the diffraction efficiency of the grating. The TM mode diffraction efficiency is more than 95%, and the TE mode diffraction efficiency is less than 5%, the pyramidal sub-wavelength polarizer grating has good polarizer performance than others shapes in the optical communication band of 1550nm. In this paper, we designed this kind of sub-wavelength grating polarizer has great potential applying in optical switching, optical memory, optical detectors and other photo-electronic devices.