Abstract: In the paper, we propose an optimized tomography based velocity model building method for pre-stack depth migration. The flow of velocity model building method for pre-stack depth migration was described. Two different tomography velocity model building methods(model tomography and grid tomography) were discussed. Applications in the same seismic data indicate that: under the high S/N ratio areas and accurate interpretation layer information provided condition, Model tomography is more accurate and stable than grid tomography.