Research on the dynamic characteristics of saturated soft soil has important significance for revealing the pore pressure, strength, and deformation mode of soft clay under subway loading. It can also provide a theoretical basis for the control of long-term settlement and the reduction of operational risk. Different forms of loading will bring different dynamic characteristic, so a study method must be identified that can reflect the true nature of subway train loads. In this study, we used the laboratory dynamic triaxial test to examine the dynamic characteristics of soil under a train load, and comparatively analyzed the effects of different dynamic loads. The results show that the biased sine wave can be used as a simplified train load wave. It also can ensure that only compressive stress exists in the soil during the process of loading, and it better simulates the cyclic loading of subways.