Dolostone is widely distributed in third section of Palaeogene Shahejie Formation from Beitang Sag in Bohaiwan Basin, which can develop good reservoir properties.In this paper, based on a vast amount of data from core drilling, rock thin sections, scanning electron microscope, electron probe and geochemistry characteristics, we study the characteristics and influencing factors of Sha 3 dolostone reservoir of Palaeogene Shahejie Formation in detail.Dolostone has four types of occurrence, including layered, nodular, massive and fracture filled.It is showed that the Sha 3dolostone reservoir rock types are mainly micrite dolostone, crystal powder dolostone and aplite dolostone.Reservoir space of Sha 3 dolostone reservoir mainly consists of dissolved intergranular pore and fractures.Dolostone reservoir is characterized by poor physical property, and the layer section with pores, caves and fractures can be performed as hydrocarbon enrichment zones.The oiliness of Sha 3 dolostone reservoir has a certain correlation with lithology and physical properties.The Sha 3 dolostone reservoir is now in the stage of mesodiagenesis, and the main diagenesis of which mainly including mechanical compaction, pressure solution, cementation, dissolution, recrystallization and dolomitization.Dissolution can be divided into three stages, and the latter two stages of dissolution lead to improve physical properties of dolostone reservoirs, while mechanical compaction and cementation result in the reducing of physical properties.Geochemistry characteristics reveal two types of dolomitization: penecontemporneous seepage reflux dolomitization and deep buried diagenetic dolomitization.Physical property of dolostone reservoir is mainly influenced by sedimentary environment, dolomitization and fracture development.Sedimentary environment plays a decisive role on the quality of dolostone reservoir and dolomitization plays an important role on the modification of reservoir space.Huge amount of fractures improves physical properties and enhances the reservoir capability of dolostone reservoir.