Because different geological structures with different properties formed in different periods were superposed together, western boundary of the Ordos Basin, especially the one in the Early—Middle Jurassic, is obscure and not easy to be discerned. So far, there has been no consensus in academy whether it located on west of the Helan Mountain or on east of the Yinchuan Basin (a Cenozoic basin situated to east of the Helan Mountain), affecting mineral resource appraisal and exploration. Based on the former research and our work, different ancient structures formed in different periods in Mesozoic are analyzed and sieved, and then the Early—Middle Jurassic western boundary of the basin is recovered. Writers consider that the huge north—south compressive structure formed in the Late Jurassic while east—west compressive structure formed in the Late Triassic. These two structures were superposed together, resulting in multiple deformations, complex superimposed structures and the irregular west basin boundary. The structure later is much clearer, appearing as a north—south thrust zone and a north—south "the Ancient Land Rise" across the basin. Since formation of the north—south compressive structure, west boundary of the basin was retreated eastward to east of the Zhuozhi Mountain thrust, the Hengshanbao—Ciyaobao fault and fold zone, the Maerzhuang thrust fault as well as the Kongdong Mountain thrust fault. However, the early compressive structure is obscure, appearing discontinuously and indistinct because of superimposing and reforming by the later. The early east—west compressive structure formed in Indosinian movement under the ancient Asian tectonic domain, while the later north—south compressive structure formed in the Yanshanian movement under the Pacific tectonic domain. During the transitional period of the Early—Middle Jurassic from the Ancient Asian to Pacific tectonic domains, the west Ordos Basin had developed nearly east—west tensional structure, forming nearly east—west uplifts and depresses, resulting in irregular instead of linear west boundary at north—south trend. Under this situation, "the ancient Yinchuan uplifts" and "the large Ordos Basin" coexisted, not controversial. The west boundary in the Early—Middle Jurassic was probably located in the Alxa Massif. The Mesozoic structures above were reformed again in Cenozoic, making the former structures more complicated and even complete destroy. Paying attention to structural analysis and sieving would be very important in the discussion on the Mesozoic structures and ancient boundaries of the basin.