A lot of oolitic model pores,biological model pores and intragranular dissolved pores were formed during syngenetic dissolution stage in the Puguang gas field,and had an effective preservation mechanism. At the first stage of buried dissolution,the acidulous water enriched organic acid with strong dissolution causes the formation of intragranular dissolved pore,intergranular dissolved pore,intercrystalline dissolved pore and cave etc. The syngenetic dissolution and the first stage buried dissolution with dolomitisation generated the main pore type of high-quality reservoir,constituted the main reservoir rocks,and coincided with the porosity change regularity; they were two key dissolution stages,were necessary and sufficient condition to the forming of high-quality oolitic reservoir. The second stage of buried dissolution mainly dissolved with CO₂ and H₂S,and the third stage of buried dissolution related to the crack and H₂S. But in thin slice,it′s seldom the mark of H₂S erosion,namely,the asphalt rim lies in the internal of pore. In Puguang gas field,the origin of H₂S has less relationship with anhydrite,source rock containing FeS₂ and sulphur in reservoirs are probably the main reason of the origin of H₂S.