Abstract: It is suggested that thick massive, stratoid and patched medium-and coarse-grained dolostones result from structural processes and hydrothermal dolomitization rather than the products of mixed-water dolomitization formed according to the current fresh-water lens model on the basis of field occurrences and microscopic and eletron microscopic analyses, oxygen and carbon isotopes, ordering and homogenization temperatures of the inclusions, in conjunction with geological evolution. The porosity of this kind of the dolostones may be great enough to serve as the oil reservoirs. It is expected to prospect and explore oil and gas deposits of porosity and porosity-fissure types in the subsurface Lower Permian dolostones.