Abstract: It was analyzed the law of the transmission and attenuation of vacuum pressure，the growth and dissipation of excess pore pressure，ground surface settlement，and the deformation characteristic and rules of layered settlement in the deep soft soil foundation covered by unconsolidated hydraulic fill of fine silty sand，and also studied the effects on consolidation deformation of the soft soil foundation covered by unconsolidated hydraulic fill of fine silt layer． Unconsolidated hydraulic fill of fine silty sand was conducive to the pore pressure dissipation and the drainage of underlying deep soft foundation． The foundation settlement was fast with fluctuation in the early stage，convergence and stability in the middle and later stage． When vacuum pressure under membrane transferred on the surface，its difference and fluctuation were large，when it passed to the deep foundation，its hysteresis and attenuation range was large． The compression of unconsolidated hydraulic fill of silty sand was large，and most of the vacuum energy was absorbed． The characteristic was not conducive to the compression deformation of underlying deep soft foundation． After treatment，the reinforcing effect of the unconsolidated hydraulic fill of silty sand was better than the underlying deep soft foundation．