The low reservoir productivity of Paleogene Shasan Member in Beitang sag is mainly attributed to its bad reservoir character. Based on large quantities of core and other geological data, the authors systematically discussed sedimentation, main reservoir characteristics of Shasan Member and the affecting factors. Sedimentary facies of Shasan Member in the study area are mainly fan delta deposition, gravity-slide deposition and lake deposition. The reservoirs belong to medium to bad reservoirs in size. Sedimentary facies, diagenetic actions such as compaction, cementation and dissolution, oil pool formation time, reservoir pressure and distribution of igneous rocks are major factors affecting the reservoir quality.