Abstract: The impulsive forces generated by waves impact is one of the primary dynamic factors influencing the safety and stability of maritime structures. In addressing the issue of wave impact on structures involving gas entrainment, the compressibility of the gas significantly influences the accurate calculation of the impact wave pressure exerted on the structures. In this paper, a numerical wave model is developed based on simplified governing equations for incompressible-compressible water-air two-phase flow, aimed at simulating strong nonlinear fluid dynamics such as wave impact on structures. The model induces wave generation by incorporating momentum source terms into the governing equations. In the present numerical framework, the convective terms are solved using a fifth-order weighted essentially non-oscillatory (WENO) scheme. Additionally, the interface between water and gas is captured using the tangent of hyperbola for interface capturing method improved by weighted linear interface calculation (THINC/WLIC). Firstly, through comparing the results of this numerical model with analytical solutions depicting the propagation and deformation of progressive waves over a flat bottom and standing waves reflected from a vertical wall, the accuracy of the present numerical model in simulating wave generation and its propagation is validated. Based on this, the model is applied to simulate the impact of regular waves on a horizontal plate. The simulated results of impact wave pressure variations on the plate are compared with experimental data and with the calculated results from a numerical model that neglects air compressibility. It is revealed that the proposed numerical model is capable of effectively capturing the influence of air compressibility on impulsive pressures during the wave impact process, and can give satisfactory results on wave impact forces both qualitatively and quantitatively. Simultaneously, the characteristics of flow field structure of simulated results at the bottom of the horizontal plate are analyzed. The analysis indicates that various shapes of gas cavity during different wave impact processes affect the velocity distribution, thereby influencing the impact pressure.