Abstract: Based on the investigation in the field and seismic profiles, we applied the theory of fault-related fold in analyzing the traps of petroleum an d natural gas in the southwestern margin of Ordos Basin. As a result, two types of fault bend folds which are suitable for traps of petroleum and natural gas were recognized, namely: (1)fault-bend folds without fore-kink bands and (2) full structural fault-bend folds. It is demonstrated that the two kinds of fault-bend folds are commonly existing in Sancha-Yanwu district of southwestern Ordos Basin and there are petroleum and natural gas traps in this area. By analyzing the geometry and kinematics of fault-bend folds, the range of traps is estimated. Another important side of using this method is to judge the tectonic stress．The main parts of the area are covered by loess layer and the base rocks are seldom exposed on the surface, especially the lower layers are fewly exposed．The authors made a preliminary analysis for the folds and faults in the basin on the fault-be nd folds theory It offers new ideas for the exploration of petroleum and gas, as well as a new method for the research of basemental geology．