Abstract: The dynamic tri-axial instrument of DTC-306 made in Japan is used to make cyclic triaxial test of silty clay under dynamical loading by load control. On the basis of various parameters and data offered from the test, utilizing common finite element procedure ABAQUS to set up the three-dimensional finite element model of the dynamic tri-axial sample, the dynamical deformation behavior of silty clay under cyclic load is simulated.Through a lot of contrast analysis to the dynamic tri-axial test relation data, the reliability of the model is validated. Then based on the finished three-dimensional finite element model, the relationship between dynamic deformation and the influence factors is researched, and the results are as follows: the first important influential factors of soil plastic deformation are initial elastic modulus, damping factor and type of cyclic load，then the magnitude of cyclic load, surrounding stress, frequency and the number of cyclic times，and the minimum influential factor is type of load wave. The numerical simulation method of finite element can substitute the dynamic tri-axial test to a certain extent.

Key words: dynamic tri-axial test, cyclic load, dynamical behavior, finite element method, numerical simulation, viscosity soil