Using numerical simulation method,we establish two-dimensional irregular wave numerical model based on the software FLUENT,and research the mechanism of wave slowly-varying force on the permeable beam-plate structure.Through simulating typical cases of wave slamming on beam-plate structures,we use low-pass filter method to obtain the slowly-varying sections from the up-lift force signals,and verify the models by comparing the experimental data with the simulation result.We analyze the influences of the three parameters on the slowly-varying force,such as wave steepness,relative clearance and relative structure width, and propose the empirical slowly-varying force formulas based on the simulation data and existing research results,which can provide reference for the similar projects.