The optimization design of structural parameters for diffraction grating is researched by combining the diffraction grating vector theory and the global optimization theory. Rigorous coupled wave analysis (RCWA) is used to analyze the grating diffraction efficiency properties, then the global optimization genetic algorithm (GA) model in the design of diffraction grating is established. The optimized structural parameters of several typical gratings including double-blazed grating in arbitrary incident angle are given. There are no special requirements for initial design and optimal groove diffraction grating structure can be obtained quickly. Optimized diffraction efficiency can reach more than 90%. Double-blazed grating can also get very high diffraction efficiency in the whole band after the optimization. The global engineering design optmization algorithm provides theoretical guidance for grating fabrication and also provides a feasible method for the inverse problem of grating design.