High-pressure water separator (HPWS) is one of the most important components of airplane environmental control system (ECS). Through introducing the Wall-Film Splashing Model into the simulation process, the trajectories of droplets, pressure drop and water separation characteristics under different condensed water contents are researched with Ansys-Fluent. Comparison with the experiment has proved that the Wall-Film Splashing Model can improve the accuracy for HPWS's simulation. Meanwhile, modeling results verified that the existence of splashing is the main cause of the relative low water separation efficiency of the HPWS. So it's of great importance to improve the design process and manufacture technique of the separation section of the HPWS in order to increase its efficiency.