Abstract: To study the collapse behaviors of silt under wave load, the stress controlled dynamic simulation tests are carried out using PFC^2D. The results show that the loading induces the collapse of silt. When the state approaches the collapse, the internal stresses of silt reach high levels and the concentrated shear stress appeares in some connected regions. But the critical strain level is not high. At the collapse, the silt still remaines to have residual strength to some extent, which is related to the level of dynamic stress. Then the effects of confining pressure and cyclic shear stress ratio on the collapse behaviors of silt are studied. It is found that with the increase of the initial confining pressure, the hysteresis loops of each group of samples show gradual tightening trends. Besides, the intrinsic reason of the development of hysteresis loops is also elaborated in the view of energy method. The research results reveal that the collapse is key to the failure forecast of silt, and they are beneficial to the analysis of the behaviors of silt around dynamic instability.