In this paper, the characteristics of Pre-Jurassic palaeogeomorphology in Ansai Oilfield have been rebuilt. On the basis of the observing of field and core, as well as the analyzing of well logs and test data, the method of mold is applied. The results of Pre-Jurassic palaeogeomorphology in studied area have been depicted as: palaeo-valley and its plain are the main geomorphic units. The Pre-Jurassic palaeogeomorphic characteristics had a great control on the sedimentary facies types and sand-body distribution in the Lower Jurassic. The north margin of the palaeo-valley and the slop of secondary valley are the location where oil and gas distribute. The slop of secondary valley should be paid attention to in the future exploration.