Abstract: The examination of stacking patterns,sedimentary sequences,sequence stratigraphy and cyclic deposition in the western part of the Xuefeng Mountains,southern China shows that just like the Sichuan Basin,the western part of the Xuefeng Mountains has gone through the basin evolution from the passive continental margin(Z-O₁) through the forelandoid basin(O₂-S) to the craton-continental marginal basin(D-T₂) and the inland lake basin(T₂-J),and finally to the intermountain basin(K-Q).Nine reginal parallel unconformities and one angular unconformity are observed,constituting five tectonic terranes,including: ① the Nanhuan to the Sinian;② the Lower Palaeozoic;③ the Upper Palaeozoic to the Lower-Middle Triassic;④ the Upper Triassic to the Lower-Middle Jurassic,and ⑤ the Upper Cretaceous or younger.In the above-mentioned tectonic terranes,there occur four first-order source-reservoir-seal associations,of which Associations I and II are believed to be favourable.The study area was originally in the favourable geological conditions,but there after underwent severe tectonic modification,especially the mountain building,uplifting and denudation from the Yanshanian movement at the end of the Jurassic onwards.It follows that the tectonic modification cited above are considered as the controlling factors of the oil and gas exploration in the marine lower association in the study area.