To study flow characteristics around square columns under regular waves，this paper establishes a non-reflective three-dimensional（3D）numerical wave flume with a mass-source wave generation method and the Reynolds time-averaged Navier-Stokes equation under the constraint of a RNG k-ε turbulence model in FLOW-3D.The built numerical model works well compared with the physical model.With the results of numerical calculations，the paper analyzes the 3D motion characteristics of the free surface around columns and the distribution characteristics of the velocity field and vorticity field around square columns.The changing law of the wave transmission coefficient Kt behind the square columns is explored using a dimensionless method.The results show that the flow field around the square columns changes periodically under regular waves，and the maximum vorticity alternately appears at the upper and lower corners of a single column among the square columns.Within the scope of the numerical simulation test，Kt fluctuates slightly with the change of the wave steepness H/L but not significantly and gradually decreases with the increase in the relative water depth d/L.