Abstract: Based on field outcrop survey, profile mapping and aeromagnetic data study, the Lianyuan sag is divided into the western, central and eastern structural sub- areas according to the structural features. The western structural belt is mainly consisted of a series of overthrust structures with SE- dipping fault planes. The major structural elements of the central structural belt are the combinations of double thrust fault system with ejective folds. While that in the eastern structural belt are imbricated thrust faults with NW dipping fault planes. In combination with the characteristics of each structural belt, the formationmechanisms of these structures are analyzed and the history of tectonic stress of Lianyuan sag is summarized.