The drilling data revealed complex development and distribution characteristics of Ordovician buried-hill carbonate reservoirs in northwestern part of Shaleitian arch, offshore Bohai Sea. According to cores, thin sections, isotope and trace elements, it is defined that the Ordovician carbonate reservoirs mainly consist of dolostone in lithology. Dissolved pores, caves and fractures are representative of reservoir space and main type of reservoirs is fractures-pores. Dolomitization, karstification and tectonism are the main factors of controlling the reservoir development, in which dolomitization is the basic factor, karstification is the important guarantee and tectonism is the key factor. The result of comprehensive seismic and geological prediction shows that the favorable Ordovician karst weathering-crust reservoirs develop in the southwest of the research area.