Abstract: Numerical simulation is an important approach to solve breakwater runup problems. This paper builds a two-dimensional Numerical Wave Tank (NWT) which was controlled by the Navier-Stokes equation based on Constrained Interpolation Profile (CIP). The control domain is solved by the fractional step algorithm for time integration. The free surface is captured using the Tangent of Hyperbola for INterface Capturing (THINC) method. The boundary of the breakwater is processed using the immersed boundary method (IBM). The problem of wave runup is considered as a solid-liquid-gas multiphase flow problem. Through the establishment of two-dimensional numerical water tanks, the numerical verification of breakwater runup is performed. Under the same wave conditions, numerical simulations of wave height rising are performed on double-slope breakwaters of different cross-sectional sizes. The results show that the model can simulate the strong non-linear phenomena such as the deformation, rolling and crushing in the wave process. The relationship between the maximum climb height and the size of the double-slope breakwater is obtained, and the corresponding breakwater is given when the minimum climb height is reached.