The radome is to ensure the antenna work normally in extreme harsh condition. It not only meets the shape aerodynamics requirement to withstand the thermal and mechanical loads during a high-speed flight, but also satisfies the electromagnetic property requirement. Electric thickness is an important electromagnetic performance index embodying the comprehensive influence of the geometric thickness, the material dielectric constant, and the incidence angle, on the electromagnetic wave transmission characteristics. After semi-finished machining, the electric thickness of the radome that is made of hard and brittle material often fails to meet the requirement owing to geometric error and non-uniformity of the dielectric constant. This electric thickness error has to be compensated through altering geometric thickness by precision grinding of the inner surface. Theoretically, the radome is a solid of revolution with a 3-D complex and curved surface. Therefore, the inner surface precision grinding is, in fact, a machining process for free form surfaces. In this paper, a digitized machining scheme and technical guideline is proposed. Firstly, the inner surface of the radome is precisely measured to set up a grinding datum. Secondly, the finishing grinding is performed based on the real inner surface and the required machining allowance. In addition, to avoid installation errors, the measuring and grinding processes are accomplished on the same machine tool for one-loading and two-operations. It is shown in practice that this technical guideline satisfies all of the performance index requirements for finish machining of the radome, effectively solving the difficult problem existed in finish machining of semi-finished radomes.