Abstract: The reunderstanding of the paelogeographic framework and the discrimination of the reef and beach facies of the platform margin constitute the key links for the breakthrough of oil and gas exploration. Based on the data available and the summarization of the related data obtained in recent survey and study, the authors carried out detailed pelogeographic mapping and researches on the important marine layers from Sinian to early Paleozoic in the middle-upper Yangtze marine basin. The results show that the middle-upper Yangtze marine basin underwent four stages of evolution: the rift basin stage (820-720Ma), the early stage of passive continental margin basin (720-540Ma, clastics shelf and primary carbonate platform construction), the last stage of passive continental margin basin (540-490Ma, the formation and evolution of the united carbonate platform), and flood platform and foreland basin filling(490-420Ma). Except for the first stage characterized by excessively high thermal evolution (Ro>3%), the other three stages had favorable conditions of oil and gas potential on the west side of the Xuefeng Mountain: reef and beach facies were well-developed in Dengying, Qingxudong and Honghuayuan periods; excellent source rocks were developed in Doushantuo, Niutitang, Wufeng and Longmaxi periods; excellent cap rocks comprising thick shale, gypsum-bearing series, and sandy clays were developed in Qiandong, Wuling, and early Silurian periods respectively. Therefore, paleogeographic mapping of the key marine layers and the important conclusions drawn above have provided important foundation for evaluation of favorable oil and gas exploration blocks in the west of Xuefeng Mountain.