Abstract: When the working condition of primary pump of pressurized water reactor (PWR) changes, water hammer phenomena appear in the loop to some extent. Severe water hammer not only would bring incident of instant over pressure and endanger the pressure boundary, but also yield the check valve failure. The contrapush check valve (CPCV) is a new kind of check valve. Its new structural design of river diversion can well reduce the water hammer phenomena, thereby enhancing the operational safety of nuclear power plant. The flow field and pressure distribution of the impact tube laryngeal and the connected cavity during the valve closing process were veritably simulated with computational fluid dynamics (CFD) simulation software FLUENT. The dynamic grid and UDF (user-defined function) technology were used in simulation. The results show that although the changes of the geometry will lead to the local flow velocity higher than that of the other part in the closing process, but the impact on the valve closing stability is very small. In addition, through the analysis of the flow field, it is found that the valve closing process can be divided into three stages, each of which shows its own independent characteristics. The study of this paper has provided a basis for future improvement of the valve structure and reliability analysis.