1. A seismic imaging method for obtaining imaging data of a subsurface structure through waveform inversion using a macro-velocity model as an initial value, wherein the macro-velocity model which is used as the initial value for the waveform inversion is calculated by: calculating a velocity difference function which is a difference between a real velocity and an initial velocity model, wherein the velocity difference function is a ratio of measured seismic scattered energy and modeled scattered energy based on the initial velocity model; and calculating the macro-velocity model by updating the initial velocity model with the velocity difference function.