The Miocene Huangliu Formation in the Ledong area is the main stratum of high temperature and ultra- high pressure natural gas exploration in the Yinggehai Basin in the north of South China Sea. Fine, medium and coarse- grained sandstones deposited by gravity water channel submarine fan are developed, with physical characteristics of medium, low and ultra- low permeability, and multi- stage and multi- type carbonate cementation. For reservoir evaluation and prediction,it is important to study the type, stage, genesis of carbonate cement and its relationship with fluid activity. The results show that carbonate cement was represented by calcite in the early, middle and late stages, and dolomite in earlyand late stages. From early to late stage, the values of δ 13 C and δ 18 O of calcite and dolomite decrease, and the contents of MnO, BaO and SrO increase. The formation of calcite in the early to middle stage was related to the dissolution and re- precipitation of bioclasts and carbonate minerals. The formation of calcite and dolomite in late stage was related to deep thermal fluid, inorganic CO 2 and organic acid decarboxylation. The dissolution and precipitation of calcite was controlled by the formation pressure and CO 2 content. The formation pressure and CO 2 content in the natural gas component are relatively high, the dissolution is strong, (iron) dolomite are developed; otherwise, the dissolution is weaker, (iron) calcite is developed.