To solve the problems of the surface pressure control precision of the low pressure casting in actual production, the original system was improved and the pneumatic servo closed-loop control system was built to control the pressure in the holding furnaces. The model of the improved system was built by using AMESim software and the parameters were set strictly, which could make the physical model close to the actual system at the most extent. Through comparing the simulation results and the experimental data, it is verified the pressure control effect of the improved system is better than the original system.