In order to study the characteristics of flow field in the process of wave impact, two-dimensional regular wave numerical models are established based on the software FLUENT. RANS equations are adopted. The standard k-ε equations are used to close the Reynolds equations. VOF method is used to reconstruct the free surface.Through three typical cases of wave slamming on open-piled structures, the models are verified by experimental data and the flow field under the structure is displayed visually. Then the parametric studies are carried out for different wave steepness, relative clearance and relative structure width. Furthermore, the relationship between the velocities of the water particle and the impact pressures is studied based on the probability analysis.