Based on the unconformity which comes from the "Anxian"orogeny, writers have studied the correlation and division for lithology and sequences stratigraphy in the Upper Triassic Xujiahe Formation in the western Sichuan Basin. At first writers researched the episodic tectonic movements of the thrust system in the foreland basin, and writers found the ununity of the characters of the accommodation change in the foreland basin. On the basis of the theory of Posamentier (1993) about the zones of the structure in foreland basin, writers divided the accommodation of foreland basin into four zones: lost zone, reduced zone, enlarged zone, and produced zone. Finally writers analyzed the four factors of the changes of the accommodation in foreland basin, which are the tectonic movements, climate changes, sediment supply, and fluvial balanced cross section. And writers consider that the fluvial balanced cross section is more important in foreland basin than in infaulted down lacustrine basin.