Laboratory tests on dynamic pore water pressure of silty soils are carried out in a new universal triaxial torsional shear apparatus of Hohai University. The influence of clay particle content and silt particle content on dynamic pore water pressure of disturbed silty soil is concluded. The mode of dynamic pore water pressure of silty soil can be expressed in a modified exponential function with two parameters a and b to simulate the severity of liquefaction after initial liquefaction. It is found that fines content has great effect on the dynamic pore water pressure of silt by the parameter b. The relationship between parameter b and silt particle content is linear

while the relationship between parameter b and clay particle content isn’t linear which reaches the maximum value when the clay content is 8 %. It is validated that modified dynamic pore water pressure mode has widely application by many tests data from both the author’s and others’.