Abstract: The calculation formulas for the wave velocities ofP_1 wave (fast compressional wave), P_2 wave (slow compressionalwave) and S wave were derivedfrom continuity of deformation and equilibrium conditionsand considering the compression of soil grains and pore fluid. According to Snell theorem, the reflectionand transmission of incident plane P_1 wave from the nearly saturatedsoil at the interface of elastic soil was studied, and curves of reflectioncoefficients, transmission coefficients, stresses and displacements of theinterface were numerically obtained. The results show that thesaturated degree is an important factor that affects the reflection andtransmission. The reflection coefficients, transmissioncoefficients, stresses and displacements change little when thesaturated degree increases by 4% from 95\% to 99%, but they changeobviously when the saturated degree increases by only 1% from 99\% to100%