Steam trap valves are mainly used in thermal power systems to pour out condensate water and keep steam inside. While during the condensate water flowing through steam trap valves, the condensate water is easy to reaching cavitation, which may cause serious damage to the piping system. In order to reducing the cavitation occupation in steam trap valves, this paper mainly deals with an optimization study. With Computational Fluid Dynamics codes, numerical model of a typical steam trap valve is established with Mixture model. The inner pressure field, flow field and steam volume fraction are all achieved under both maximum flow rate working condition and regular working condition. Based on the cavitation results, the throttling stages of the steam trap valve are optimized. And the results show that cavitation range inside the steam trap valve is reduced.