The key parts are the stator and the rotor to realize the function of single screw hydro-mechanical. Along with the further improvement of performance requirement of mechanical product, it’s obvious that the general screw mechanical with rubber bushing stator can’t meet the requirement. So the process technology of inner helical curved surface with metal stator becomes the key technology to improve the screw mechanical property in the world. Considering the special structure of single-screw pump stator bush, a new method enveloping boring without instantaneous velocity center was presented in this paper. Based on motion principle of screw bush pairs and practical theory of enveloping boring without instantaneous velocity center, this method realizes the boring machining for inner spiral surface of stator on NC machine. In this paper, the motion regular pattern of screw in bush was studied, and the basic principle of enveloping boring without instantaneous velocity center was represented. In the end, the feasibility of this method was proved. The new method provides a theoretical basis for the machining of stator inner helical curved surface and the development of machine tool.