Abstract: The coastal sedimentary silty soil is easy to be liquefied under wave action. In recent years, this issue has become a common concern of studies. Since the silty soil contains certain amount of clay, its liquefaction mechanism is different from sands. Through dynamic triaxial experiments carried out for the silty soil with different clay contents, we obtained the relation curve between pore pressure and strain. Take ε=5% as the criterion for soil failure, we discussed the results of experiments in this paper together with the micro-texture of the soil. It suggests that the liquefaction of the silty soil includes two types of mechanisms, i.e. liquefaction and thixotropy, depending upon clay contents.