We use the VOF（volume of fluid）method to trace the water surface，simulate the wave generation by the wave paddle method，establish a numerical wave tank to study the relationship between wave transmission coefficient and various influencing factors of the closely arranged pile breakwater，analyze the influence of pile diameter，clear distance，perforated ratio and wave steepness on wave transmission coefficient，and establish a formula for calculating wave transmission coefficient of closely arranged pile breakwater by regression analysis based on the results of the numerical simulation and the physical model test. The results show that the wave transmission coefficient of closely arranged pile breakwater decreases rapidly at first and then slowly with the increase of pile diameter，and increases rapidly at first and then slowly with the increase of clear distance and perforated ratio. In the case of submerged，the transmission coefficient increases with the increase of submerged degree and tends to be stable. In the case of non-submerged，the transmission coefficient increases at first and then becomes stable with the increase of the gap between freeboard height and water level. The wave steepness has no obvious effect on the wave transmission coefficient.