Abstract:Wave equation time migration fails to image subsurface geological structure correctly in the case of obvious lateral seismic velocity variation. Consequently, people have begun the study of depth migration. Fay using pseudo differential operator, a wave equation can he split into a diffraction equation and a time shift equation. The migration range can be increased to 60º by approximating the diffraction equation to 45º one-way wave equation, with the coefficient modified. The introduction of auxiliary function makes the 45º equation change into low order partial differential equations, which can he easy solved using difference method. This method takes 1.5 times the operation of 15º equation time migration. It is a fast and practical depth migration method.