In recent years，there are many discoveries of oil and gas in Neozoic in Bohai oilfield，but the exploration degree is relatively low for Paleozoic carbonate buried hill. There is a good oil discovery in Paleozoic in Well Bozhong21-2-A.Lithologic types of Paleozoic carbonate were determined as mainly dolomite，limestone，dolomitic limestone，calcite dolomite and mudstone through analyzing data of drilling，coring，logging and testing from Well Bozhong21-2-A in Paleozoic carbonate buried hill of Bozhong21-2 structure and by combing with petrology，mineralogy，geochemistry and other experimental data，it was concluded that the physical properties of dolomite are better than that of limestone. There are three types of storage space which are pore，karst cave and fracture. The main reservoir type is karst cave reservoir which can be divided into three sections in vertical，and the karst cave reservoir mainly develop in upper and lower Paleozoic，while the karst cave-fracture reservoir mainly develop in middle Paleozoic，and the sedimentary facies，karstification and structure regmagenesis control the development of reservoir. The research shows that the favorable sedimentary facies of intra-platform and beach develop in Bozhong21-2 structure. The center of buried hill locates at the highland of karst plateau and karst slope without Mesozoic covering，which is easy to be karstified and become favorable paleo-karst reservoir.