The deformation of roadbed and control of post-construction settlement are great challenges in widen subgrade projects because of the long-term deformation effect of soft soil. The stability and deformation of the case in the condition of different dumping thickness and filling velocity was discussed,based on the FEM model for soft soil subgrade of new building Pukou highway. The result shows that the post-construction settlement and the differential subsidence of pavement increased with the increasing filling velocity. In this situation,pore water pressure is not easy to dissipate,so the soil consolidation rate decreases. To accelerate project schedule,drainage board should be built up in time. And the differential subsidence of pavement under the same filling velocity is increasing when the dumping thickness increases.