Using the multifactorial analysis of identification of boundary sequence and depositional sequences, the Xujiahe Formation in NE Sichuan can be divided into two extremely long and five long baselevel cycle sequences. The sequence structure and evolution of both sequences have clearly reflected the coupling process between basin and mountain of the Xujiahe Formation of Upper Triassic in the northeastern Sichuan foreland basin. It is characterized mainly by lowamplitude uprising of the MingcanshanDaban orogenic belt during the lower basinforming period of T3x2 T3x3 member, and by lowamplitude subsiding of the northeast depression. Material supply was basically balanced with the low amplitude of accommodating space. Braided river delta  lake sedimentary system was main system developed, and its sequence is characterized by that the thickess of rising equals to that of subsiding, reflecting a relatively stable coupling of basin and mountain. During the upper basinforming period of T3x4 T3x6 members, the MicangshanDabashan Mountains entered an stage of intensive thrustingnapping and uplifting, resulting in a sudden, rapid subsidence of the foreland basin in NE Sichuan. Clastic sediments increased so dramatically that accommodation space was unable to store. Therefore, alluvial fanfan deltabraided river delta sedimentary system developed, with uplifting thickness more than that of subsiding. The rising cycle of baselevel sedimentary sequence, retained in the front of orogenic belt, is asymmetric, reflecting a great imbalanced coupling process of basin and mountain with the baselevel sequence uplifting and subsiding.