The Xar Moron River Fault is the final suture between the North China Plate and the Siberia Plate. Based on the available high precision age data from the basement of the Songliao Basin, the reinterpretation of the gravity anomaly and MT profile, the characteristics of the lithosphere and crustal thickness of the northeast margin and the neighboring areas of the North China Plate, the authors revealed the distribution of the Xar Moron River Fault under the southern Songliao Basin, which extends from Kailu, Tongliao, Horqin Zhuoyizhongqi to Changchun.