Abstract: To gain more insights into the microscopic mechanism of the liquefaction behavior, the particle flow program PFC^3D is used to simulate the liquefaction process of silty sands under undrained cyclic loading. The effects of the initial static shear stress and fines content on the cyclic liquefaction behavior of sand are investigated. The simulation responses of silty sand containing a small amount of fines are compared with those of clean sand under the same initial state parameters. The simulated results show that regardless of the fines content, different initial static shear stress conditions can result in two liquefaction failure patterns: cyclic mobility and residual deformation accumulation. Generally, the samples exhibit cyclic mobility accompanied by a decrease in the coordination number. The coordination number of samples under residual deformation accumulation changes slightly, while the fabric norm F is always greater than zero as the cyclic shearing proceeds. Under the identical initial state and stress conditions, the coordination number variation of fine-grained sand during cyclic loading is larger than that of clean sand, and its liquefaction resistance is also larger. Furthermore, a higher initial static shear level leads to a larger change in the coordination number and also an increase in the cyclic liquefaction resistance.