Abstract: Yakenbei area in Kuqa depression is characterized by high?relief, non?homogenous distribution of deep geological body with special lithology and complicated geologic conditions in surface and subsurface. They are the main reasons for influencing velocity analysis and the trap?scale determination in this area. The conventional research of trap study by seismic data is based on the fixed datum, but the errors between forecast depth by seismic data and actual drilled depth are normally big. So, the velocity?varied mapping technique based on the floating datum in this area is proposed and carried out. The result indicates that the predicted precision by this method is much higher than that by using fixed datum, providing powerful tool for trap study of complex areas