A set of dark fine-grained shale of semi-deep water-deep water shelf developed in the Wufeng Formation-Longmaxi Formation in Southeastern Chongqing. Based on the fine study of lithofacies, nine types of lithofacies are divided from Wufeng Formation to Longmaxi Member 1: carbon-rich & silicon-rich & graptolite-rich shale facies, high-carbon & high-silicon & graptolite-rich shale facies, medium-carbon & high-silicon & high-graptolite shale facies, low-carbon & medium-silicon & graptolite-containing laminated shale facies, medium-carbon & medium-silicon & graptolite-containing shale facies, low-carbon & low-silicon & graptolite-containing shale facies are six major lithofacies; low-carbon & low-silicon shell limestone facies, low-carbon & low-silicon dolomitic shale facies, and low-carbon lime argillaceous siltstone facies are three secondary lithofacies. Carbon-rich & silicon-rich & graptolite-rich shale facies and high-carbon & high-silicon & graptolite-rich shale facies are the optimal lithofacies, which have the characteristics of high organic carbon content, high porosity, high brittleness, high gas content, and development of micro fractures. When the horizontal well passes through the optimal lithofacies, the gas production of single well is high. The optimal target window for horizontal well in different zones is clarified, which lays a foundation for better guiding the trajectory of horizontal wells.