Based on virtual soil pile model, the influence of sediment properties on complex impedance at the head of rock-socketed pile is theoretically investigated by virtue of Laplace transform technique and impedance function transfer method. Firstly, the sediment under pile toe is assumed to be virtual soil pile which the cross-section area is the same as the pile. The layered soils surrounding pile are described with plane strain model. Then, by means of initial conditions and boundary conditions of the soil-pile system, the complex impedance at rock-socketed pile head in frequency domain is derived at condition of arbitrary excitation on the pile head. At last, by using parametric study method, the influence of sediment properties on complex impedance at rock-socketed pile head is studied. It is shown that sediment properties have significant influence on complex impedance at the head of rock-socketed pile.