The invention discloses a speed splicing method and a speed splicing system for pre-stack depth offset. The method comprises the steps of based on seismic data, acquiring an observation travel time ofa preliminary wave, an initial speed model and a deep-layer speed model; based on the observation travel time of the preliminary wave and the initial speed model, obtaining a shallow-layer speed model through the grid tomographic inversion process; based on the shallow-layer speed model, obtaining the bottom boundary of the speed inversion; based on the deep-layer speed model, the shallow-layer speed model and the bottom boundary of the speed inversion, obtaining a depth offset speed model; performing the pre-stack depth offset based on the depth offset speed model, and obtaining a pre-stackdepth offset result. According to the invention, the shallow-layer speed model obtained through the grid tomographic inversion process and the deep-layer speed model obtained through the pre-stack time offset process are spliced, so that the high-precision pre-stack depth offset imaging is achieved.