Abstract: In Chezhen area the tectonic analysis and stratigraphic investigation show that the paleokarst depth within a buried hill is shallow,while the paleokarst depth along the periphery of the buried hill is deep.Petrologic and geochemical methods are fully made use of to study the paleokarst,and three periods of paleokarst are recognized,i.e.the paleokarst during the sedimentation of the Yeliliangjiashan-Fengshan group,the Caledonian one,and the Indosinian-Yanshanian one.The paleokarst mechanism is then discussed.The paleokarst during the deposition was controlled by sedimentation and diagenesis.Its favorite accumulation space is formed by dolomitization,whose diagenetic fluid is rain and sea water.The Caledonian paleokarst is formed by rain water.Its paleokarst happened mainly on the surface of the zone,and the solution fracture,pore,and cavity are later filled with C-P mudstone.The Indosinian-Yanshanian one is the main paleokarst of the study area.It is controlled by tectonic movement and stratigraphy.The solution fluid is mainly rain water mixed with the hot water underground.