Abstract: In order to study the influence of silica fume on the mechanical properties of soft soil, silty clay samples from Yinzhou district, Ningbo were mixed with different amounts of silica fume to test the mechanical properties and structure characteristics. The relation between stress and strain of stabilized soil with different content of silica fume was tested by triaxial undrained tests, and the structural characteristics were analyzed by SEM. The results show that the silica fume can improve the cohesion of soft soil, and the cohesion increases with the addition of silica fume. With the increasing content of silica fume, the anti-deformation of silica fume stabilized soil increases at the beginning and then decreases, and the damage deviator stress of silica fume stabilized soil increases under the same confining pressure. Increasing content of silica fume leads to the decreasing number of the larger pores and the increasing number of the smaller pores in silica fume stabilized soil, and the proportion of pores dominated with diameter is less than 1 μm dominated gradually.