The radome made of special ceramic is a workpiece needed to be machined precisely. The machining precision of the exterior contour of the workpiece effects the performance of the radome directly. Around improving on machining technology of the traditional radome’s exterior-surface, the creep feed surface grinding by cup wheel based on line enveloping is presented in this paper. Due to combining the advantages such as large material removal rate, high machining precision and high efficiency of creep feed grinding and the superiority of cup wheel, the workpiece with perfect surface quality can be reached. Furthermore, the mathematics model of the geometric locus of grinding wheel head rotating center is established by using the linear interpolation algorithm, with a combination of the equal-space and equal-error method. The existing NC grinding machine with 2-axis simultaneous motion is transformed into 3-axis simultaneous motion (adding an axis of rotation B) and its feasibility applied to the exterior contour machining has been verified.