Abstract: According to karstification time, depth, rocks medium, producing environment and mechanisms, karst can be classified into karst and paleokarst, and in vertical it also be divided into five belts including weathered layer, vertical seepage belt, seasonal changed belt, horizontal seepage belt and deep sluggish belt based on the features of karst's hydrodynamics. After summing up the former researchers' results, it is discussed that 10 geological factors are related to develop the paleokarst of oil-gas reservoirs and 7 kinds of karst developing mechanism, and is concluded the progress and the development tendency of karst research in the future