By means of core observation, thin-section identification as well as carbon and oxygen isotope analysis, the reason for the differences of karst reservoir generation between well XG1 and well XC1 in buried hill of Xinghua city of the North Jiangsu Basin has been studied, and the formation mechanism of karst reservoir in buried hill has been concluded. The explorations for buried hill reservoir should be focused on the passive side of border fault of sag, and the saddle between low uplifts of Mesozoic-Cenozoic as well as the Lower Paleozoic crystalline dolomite buried hill below slope.