Abstract: The structures of mountain front in southern Junggar basin are complex and the variation of lateral velocity in deep formation is considerable. In order to improve the accuracy of structure mapping, varying velocity mapping technique was used to map the structures. Firstly, the T0 layer data of post-stack time migration domain (abbreviated in migration domain) was de-migrated into common-depth-point-stacking time domain (abbreviated in stacking domain). Then, stacking velocity inversion method was used to obtain the horizontal velocity responding to the grid points of T0 layer data in stacking domain; finally, 3-D ray map-tracing migration method was applied to convert T0 map into depth map. The varying velocity mapping result was compared to simple time-depth relationship transformation result, showing that the varying velocity mapping technique can effectively improve the accuracy of structure maps and an anticlinal trap was discovered in the south of the working area.