In order to obtain high performance of polarization splitting grating, the subwavelength sandwiched metal grating structure was designed and analyzed. The optimal grating parameters were made by using the rigorous couple wave theory and genetic algorithm. Based on the optimized grating structure, high diffraction efficiencies of 98% and 96.5% can be achieved for TM transmission and TE reflection of 0th order in the 800 nm wavelength range, respectively. The optimized grating has an extinction ration of over 20 dB from 747 nm to 854 nm, and a large angle, from -27° to 27°, which met the expectations for high efficiency, high extinction ratio and wide spectrum and large angle. The fabrication tolerance around the optimized grating parameters was discussed, numerical results showed that the designed grating has good manufacture tolerance to period and groove depth and covering layer thickness. The subwavelength metal grating own many good characters such as simple structure, stable performance, low damage for the incident wave and obvious polarization, which will make the subwavelength metal grating have wide application prospect in the fields of optical polarizing elements, laser system, polarization imaging, etc.