Existing color separation diffraction grating spectroscopic methods are generally discussed on parallel incident light,and there is little discussion of the case of non-parallel incident light.Based on the Fresnel diffraction theory and the angular spectrum theory,the spherical wave propagation field and plane wave diffraction wave field are linked together,and angle function parameters are imported.Combined with fractional Talbot effect theory,the dual-wavelength wide-angle incident wave field function is derived.The numerical simulation of the function is presented to calculate the diffraction distribution in different locations,which are compared to standard parallel incident wavefield distribution and calculated horizontal broadening and offsets.By adjusting the width of grating steps，the diffraction field broadening and offset is compensated.Each single-wavelength diffraction width is less than half of the grating period,thereby reducing the dual-wavelength optical diffraction aliasing.In this paper,the relation between the wave field width and grating step width is presented.The step width curve is fitted based on multi calculate points on the phase grating and the grating parameter can be used to achieve well spatial separation of dual-wavelength wide angle incident light.The result is available for a variety of wide angle incident situation,such as dual-wavelength imaging,LCD display,LCD projection,etc.