The constitution and characteristics of the releasingpressure system of Warm IsostaticPressure (WIP) machine were studied. The mathematic modeling of control system by theory identification was gotten, and the application of fuzzy control arithmetic on the releasing-pressure system of WIP machine based on the different aperture combinational valves was studied. The fuzzy illation software FIS was used to design fuzzy controller, which was embedded into the simulation platform to build up the simulation platform for releasing-pressure system, and to carry out simulation experiment for five common-used techniques curves of following control. The simulation results show that the fuzzy control arithmetic can meet the requirements of wide-pressure extent and high-precision curve controlling of the releasing-pressure system of WIP machine.