Zinc selenide polyhedral reflection prism is an important component of the optical system of a roll-pitch long-wave infrared seeker, which directly affects the imaging quality of the optical system. For prism’s complex polyhedron plane structure and the feature of polycrystalline zinc selenide material, a precision processing of single point diamond fly-turning is proposed. A mathematical model is established for the position relationship of each surface of the prism, and a special tooling to ensure one-time clamping and processing is designed. The turning path is simulated, and the effects of parameters such as spindle speed, cutting depth and feed rate on the surface quality of ZnSe are obtained through experiments. The parameters of the reflection prism is obtained, such as 12″ angle error, PV:0.13 λ surface shape error, 0.02 λ RMS, Ra:7.39 nm surface roughness and Ⅴ surface imperfections. The design requirements are met. And the process method of precision processing ZnSe polyhedral reflection prism by fly-turning is verified.