1. A seismic imaging system using Laplace-domain wave equation in acoustic-elastic coupled media, comprising: Scaled gradient calculating unit calculating a scaled gradient direction of an objective function by multiplying a gradient of the objective function and a accumulated gradient which is calculated using a vertically accumulated square sum of the original gradient values, wherein the objective function is defined by a residual of logarithmic wavefield in Laplace domain; Modeling parameter updating unit updating the model parameters for a discretized finite element equation for acoustic-elastic coupled media from a Laplace-transformed acoustic wave equation, a Laplace-transformed elastic wave equation and continuity conditions at the interface between the acoustic media and the elastic media; and Iteration control unit controlling the scaled gradient calculating unit and the modeling parameter updating unit to repeat processing iteratively until a stopping criteria is met.