Abstract: The uplift of the Tibetan Plateau in the Cenozoic has changed the tectonics of the whole Asia and affected the climate and environment significantly. However, the mechanism of the plateau uplift and expansion is still in debate. The southeastern margin of the Tibetan Plateau, as the one of the expansion frontiers, provides the key to understand the tectonic evolution of the plateau. In this study, we review the progress of the researches on the crustal structures in the southeastern plateau margin, especially those achieved after the ChinArray project since 2011. The latest results show that the thickness of the crust descends from the plateau to its southeastern margin with an abrupt change under the plateau boundary. Two independent low-velocity zones are revealed in the lower crust: one under the Songpan-Ganzi terrane which is part of the high plateau, and another orientating NE-SW under the Xiaojian fault zone. We propose that the lower crustal materials extruded from the high plateau are blocked around the plateau margin (i.e., Lijiang-Xiaojinhe fault) by a strong crustal block in the western margin of the Yangtze block. However, the stress is further transferred to the Xiaojiang fault zone and induced the crustal deformations there.