Based on the integrated procedure requirement for multi-stage CNC machining, the present thesis purports to analyze the machining process for case shells through position distinguishing method for machining surface of case shells. Given that there are quite many case shell machining positions, the machining process includes broaching, drilling, tapping, reaming and boring. To accomplish the multi-station and multi-stage machining in one clamping，a fixture that can utilize the function of the horizontal NC machining center machine is designed. By optimizing the specific structure of the fixture, pneumatic quick clamping mechanism is adopted to realize high efficiency, high precision and reliability.