Abstract: In 3 -D prestack depth migration. iterative modifications of velocity models and depth models arc performed through directional depth migration and 3 - D tomography to set up accurate layer velocity model thus realize accurate imaging. Appraisal wells are drilled in Benbutu area of Yanqi basin and Liyuan area of Biyang depression based on the 3 - D prestack depth migration interpretation results. The error between the predicted depth and actual depth of the targets is only 3 to 7m.