Taking the Kenjiyak Oilfield in Kazakhstan as an example, the fracture characteristics and genetic mechanism of carbonate reservoirs with overpressure were discussed. The study showed that carbonate reservoirs are formed under overpressure developed hydraulic fractures besides tectonic fractures and karstic fractures. Hydraulic fractures are mainly the extensional fracture, which has late opening time and low filling degree, thus is the main effective fractures in the study area.