Neutron polarizing supermirror (NPS) is a primary optical device for polarizing neutrons. In this paper, an optimized design method of NPS based on the famous Mezei design method, which has been widely applied in the design of neutron supermirrors is presented. Firstly,this paper introduces the principle of NPS, bringing up a method to choosing the material of layers in the NPS. Secondly, the Mezei method, which was brought up by Mezei in 1976 is introduced. Thirdly, two optimizing methods are presented for overcoming the shortages of Mezei method. Finally, the FeCo-Si neutron polarizing supermirrors are designed based on the optimized method for good reflectivity and polarization. The calculation results show that both methods can improve the reflectivity of the spin-up neutrons and the polarization.