Many normal-pressure giant gas ifelds have been discovered in the Ying-Qiong Basin, South China Sea, e.g. X1-1 and Y13-1. However, the hydrocarbon accumulation mechanism of HTHP natural gas reservoirs are not ifgured out due to poor-quality seismic data of middle-deep layers, complex HTHP geological conditions and high-dififculty drilling and completion engineering. And as a result, the exploration discovery of HTHP natural gas in the Ying-Qiong Basin is seriously restricted. This paper is aimed at ifnd-ing out the key theories on HTHP hydrocarbon accumulation mechanism of the Ying-Qiong Basin. A series of studies were carried out by using drilling, geological and seismic data, including hydrocarbon generation of source rocks under high temperature and pressure, natural gas dissolution experiment, sedimentation model of large reservoirs under high pressure and temperature, and sealing mechanism of cap rocks. It is indicated that the high temperature ifeld in the Ying-Qiong Basin promotes the gas generation of organic matters, and the high pressure inhibits the gas generation of organic matters in the early stage, but promotes in the late stage. Under high temperature and pressure, natural gas can be exsolved in the form of free gas. In the Ying-Qiong Basin, large non-restricted gravity-lfow submarine fan and restricted gravity-lfow channel sand reservoirs are developed. In the Ying-Qiong Basin, the hydrocarbon accumulation and enrichment of high-pressure gas ifelds is controlled by overpressure sealing. Finally, the hydrocarbon accumulation pattern of HTHP natural gas reservoirs was established as “hydrocarbon generated by land-derived marine source rocks, gas accumulated in gravity lfow reservoirs, gas transported along fractures/overpressure ifssures and gas sealed by overpressure cap rocks”. The research provides theoretical bases for exploration breakthrough of HTHP gas reservoirs in tne Ying-Qiong Basin, and they are used as the reference for the discovery of large and medium high-pressure gas ifelds, such as X13-1/X13-2 and L25-1. In the Ying-Qiong Basin, a series of large, deep high-pressure sags are developed and the overall exploration degree of middle-deep reservoirs is lower, so the potential of natural gas resources is immense.%南海莺-琼盆地已发现X1-1、Y13-1等多个常压大气田，但受中深部地震资料品质差、高温高压地质条件复杂及钻完井工程难度大等限制，高温高压领域天然气成藏机理认识不清，严重制约了莺-琼盆地高温高压领域天然气勘探发现。以破解莺-琼盆地高温高压条件下成藏机理关键理论问题为核心，利用钻井地质、地震勘探资料，开展了高温高压条件下烃源岩生烃、天然气溶解实验、高温高压领域大型储集体沉积模式和盖层封盖机制研究。研究认为：莺-琼盆地高温场促进有机质生气，高压早期抑制、晚期促进有机质生气；高温高压条件下天然气能够出溶形成游离气；莺-琼盆地发育大型非限制型重力流海底扇、限制型重力流水道砂储集体；超压封盖控制了莺-琼盆地高压气田的成藏富集。构建了“陆源海相烃源岩生烃、重力流储集体聚气、断裂/超压裂隙输导、超压盖层封气”的高温高压天然气成藏模式。研究成果为莺-琼盆地高温高压领域勘探突破提供了理论依据，指导了近年X13-1/X13-2、L25-1等大中型高压气田的发现。莺-琼盆地发育的一系列的深、大高压凹陷且中深层整体勘探程度较低，尚有规模巨大的天然气资源量待发现。
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