Abstract:Because Hailar-Tamtsag Basin is a Mesozoic-Cenozoic rift basin, and developed on the basis of Tianshan-Xing'an Variscan orogenic system. And Hailar-Tamtsag Basin was strongly influenced by the late tectonism, the architecture of the basin and its evolution is very complicated, the advances in fundamental geological researches are slow, and seriously impede the progress of oil and gas exploration. Based on the 3D seismic data of Nanbeier Sag, a structural analysis for the working block is conducted, the architecture characteristic of the sag is found out, the regularity of the tectonic evolution is summarized, and the tectonic formation mechanism is analyzed on the basis of the system interpretation of 3D seismic data. And the structural styles of Nanbeier depression can be divided into five groups, that is, weakly rifting stage, intensely rifting stage, reversely compressing stage, transtensional depression stage, and transpressional depression stage. It has an important significance for the geologic understanding of Nanbeier sag and even the whole Hailar-Tamtsag Basin, and accelerates the oil and gas exploration process of Nanbeier sag.