Qiangtang Basin is situated in the North Tibet plateau. Its north and south boundaries are Lazhulong-jinshajiang suture belt and Bangonghu-nujiang suture belt respectively. The area of the basin is about 160,000km2. Paleozoic to Mesozoic (especially Jurassic) marine strata is well developed in the basin. Dolostones are widely distributed in the middle series and the bottom of upper series of Jurassic. They are the most potential oil & gas reservoir rocks. The dolostones can be classified into two types (i.e. type 1 and type 2) according to their origin and the characteristics of rocks & minerals. Type 1 dolostone was formed in the evaporation condition by way of capillary concentration dolomitization. It is associated closely with gypsum (anhydrite). Dolomite crystals in the dolostone are very thin or little. Its chemical composition is relatively rich in Ca2+.  The degree of order of its crystals is fairly low. Type 2 dolostone was formed in the mixed waters of marine water and meteoric fresh water. It is not associated with gypsum (anhydrite). Dolomite crystals in it are thicker and more euhedral than that in type 1 dolostone. The chemical composition of type 2 dolostone is relatively rich Mg2+. The degree of order of its crystals is fairly high. Type 1 dolostone was not obviously remade after it was formed. It keeps low to mid porosity and very low permeability as it was in original. Type 1 dolostone can form oil and gas reservoir with ranks II-III in the basin. After it was formed, type 2 dolostone underwent clear recrystallization and dissolution, and filling and replacement by calcite in late-diagenetic to epidiagenetic stages. Type 2 dolostone, especially that was not remade by epidiagenesis, can form oil and gas reservoir with ranks I-II in the basin because of its fairly good conditions of porosity and permeability.