The pump body of nuclear cooling pump is one of the three core parts in the main loop system. The manufacturing precision of pump body has a direct influence on the operation safety of the whole equipment. In order to improve the machining precision of the pump body, a five-axis CNC machining process was proposed. The characteristics of the pump body were analyzed, the dimensional tolerance was applied to modeling, and the special fixture was designed. Based on genetic algorithm, the processing technology and method were studied. Five-axis linkage CNC machining center was used to complete the processing of nuclear cooling pump body. The processing problems such as cylindrical inverted face, 90° pipe bending and thin wall were solved.