The head of piston must be machined avoid the pit, so that the piston can have some clearance during movement. Taking the processing of avoiding valve pits of the variable rounded piston as an example, the parameters setting, the processing process preparation and NC code generation were completed by using MasterCAM software. And the actual processing was completed. The influence of different programming methods on the machining of the piston avoiding valve pit was analyzed. Finally, the optimal machining method was determined.