A method of designing antireflection multilayer using the theory of inhomogeneous coatings was presented. The cause of difference of transmittance is analysed by polarized light and in the case of incidence at wide angle. Antireflection multilayer of 500～600 nm at incidence angle from 0° to 80° have been designed using Ta2O5 and SiO2 as materials of refractive index of smultilayer, using BK7 as material of substrate. A new way of film design has been explored. It shows the result of optimization is perfect. This method can increase the ratio of utilization of optical energy, and it can find the applications in the fields of solar energy, optical fiber communication, aerospace industry, laser and so on.