For investigating the subgrade settlement of the foundation，the piezocone penetration test (CPTU)was performed on field penetration at an expressway subgrade in Hunan Province. Based on the relationship between soil parameters and the penetration data，the parameters of the modified Cambridge model of foundation soil was obtained，and the finite element model was then established considering fluid-structure interaction of the foundation soil of subgrade. The settlement of subgrade during filling construction was calculated and compared with the measured value. The results show that the settlement calculated by the CPTU is consistent with the measured settlement，the subgrade settlement mainly occurs in the filling period，and gradually decreases with the increase of the depth. The settlement is basically stable about 1 year after construction.