Abstract: With regard to the pile foundation in soft soil, because of the downward movement of the soil around the piles, the friction between the soil and the piles increased the downdrag of the piles, and it was called the negative skin friction. The result is that it increases the deformation of piles and even leads to the destruction of pile foundation. The first-hand materials about the change of the axial force of pile is obtained during and after embankment fill behind abutment in soft ground by the field test of the piles, and it reveals the variation of the internal force of pile and the negative skin friction. Test results show that the influence of embankment fill on the axial force of piles exist not only during the construction, but also a long time after the construction. The axial force of piles first increases with the depth and then decreases. The variation of negative skin friction with the depth of piles is nonlinear.