In order to overcome the molding technology of high-steep spherical optical parts, a sub-aperture grinding method was proposed, taking the hemispherical and hyper-hemispherical infrared optical domes as the research object. The traditional generating method grinding forming theory is expanded, the spherical surface is discretized into a series of sub-aperture rings, the grinding wheel "steps" along the ring, and a complete spherical surface is obtained by splicing and forming. In this paper, the transformation relationship between the forming spherical surface and the position coordinates of the three-axis machine tool was analyzed, the machining motion trajectory was simulated, and the radius error compensation verification experiment and the variable feed parameter optimization experiment were conducted. A method of variable radius grinding was proposed to solve the problem of over-cutting of hyper-hemisphere machining materials. The forming process test was carried out on the hot-pressed zinc sulfide and magnesium-aluminum spinel spherical dome with the aspect ratios of 0.5 (hemisphere) and 0.55 (hyper-hemisphere) respectively, the sag height difference of each point on the processing surface < 4 μm, and the surface roughness Ra<1.5 μm. The results show that the method is feasible and can provide an effective solution for deep high gradient spherical processing.