Abstract: In this paper, we discuss the imaging principle and key technology of pre-stack depth-migration in 3D seismic exploration.The 3D pre-stack depth-migration technology may realize the correct spatial homing of the reflection point and the stacking of the real common-reflection-point, which decreases the extent of the Fresnel zone and greatly improves the resolution of seismic data.In the actual seismic data processing and applications, the breaking points of small faults of this technology are more clearly displayed than that of the pre-stack time-migration technology.So the technology of pre-stack depth-migration can improve the ability of 3D seismic exploration in detecting mini-structures and has achieved a good geological effect.