A method of designing antireflection coatings by the way of Rugate coatings was presented. The reason of difference of transmittance was analysed under the circumstanes of polarization and board angle incidence. Antireflection coatings of 1500-1600nm and incidence angle from 0° to 80° were designed. A new way of design was founded. It shows that the result of optimization is perfect. This method can increase the ratio of utilization of optical energy. It has great value of application in the fields of sun energy, optical fiber communication, spaceflight, laser and so on.