Abstract: The piers of coastal bridges often suffer from the slamming of breaking waves, and particularly the slamming load of plunging breaking waves threatens the structure safety. The plunging wave slamming load on square piers was studied by both theoretical and experimental investigation. Based on the empirical calculation formula of structural slamming load and MLM theoretical model, a theoretical calculation model of plunging wave slamming load on square section pier is established. The relationship between slamming angle and slamming load is explored by the plunging wave breaking flume test. The effectiveness of the theoretical model is verified by comparing the slamming pressure-time history of the square pier section under different slamming angles. Combined with the test and theoretical model, the range of the curling factor of the square pier subjected to different slamming angles is determined. The results show that, a smaller included angle between the slamming direction of plunging breaking wave and the water facing the axial direction of the square pier leads to larger slamming load, and the theoretical model presented in this paper can well describe the variation of slamming pressure-time history with slamming angle, also the variation formula of curling factor of square section with slamming angle is obtained according to the experimental results.