A mathematical model of air bubbles breakwater to research the wave dissipating performance is presented in the paper. The model is established based on the assumption that the two-phase fluid of water and air is a variable density fluid. In addition, a mass source term is added to the continuity equation and a momentum source term is added to the momentum equation by the Macro of UDF (User Defined Function). Comparison between the computational results and experimental results illustrates that the mathematical model is reasonable. Other influencing factors such as the incident wave height and the submerged pipe depth are taken into account and the numerical simulation results are analyzed. Conclusions are referential and meaningful for the design and construction of air bubbles breakwater projects.