A new type of waveguide collimated projection system uses diffraction grating, which can complete the beam coupling, expansion and imaging by only using one waveguide plate. So it is more conducive to system integration and miniaturization, and it has great research value. A Matlab model of the diffraction grating in the new type of waveguide collimated projection system is established based on the rigorous coupled wave theory. According to the performance requirements of the system, the models of the coupled grating, extended grating and exit grating are analyzed, and the structure and related parameters of the diffraction grating are designed. The results show that the new blazed grating is used as the coupled grating, and the extended grating is designed as a combination of traditional binary grating and novel binary grating, while the output grating is a blazed grating. The waveguide collimated projection system is uniformly imaged, whose field of view is 24.8°×30°. The system can be used for the integrated and miniaturized displays with small occupation and light weight.