Abstract: Fracture is a good hydrocarbon reservoir space and migration channel, but there is little research on the difference of fracture strength among different rocks that affect the formation of fractures. Based on core observation and thin section analysis, the fractures in the Paleogene-Neogene of Zhanhua sag were classified. By using triaxial rock mechanics test, the rock fracture strength was compared and analyzed. The results show that the fracture is mostly developed at the interbed interface of different lithologies. Under the action of vertical pressure, the fracture strength is successively carbonate, mudstone and sandstone.