Abstract: The Yinggehai Basin is located in the Yinggehai sea between Vietnam and Hainan Island. Up to now, only have the shallow gas fields DF1-1 and LD15-1 and several others been discovered. However, the exploration of medium-deep layers of hydrocarbon remains very low. So far, only have the DF13-1/13-2 structural-lithological traps got gas breakthroughs in the Dongfang area. In this paper, by analyzing and studying the geological conditions and main controlling factors of shallow gas fields in Dongfang and Ledong areas, we discussed in depth the characteristics of the source-reservoir-cap assemblages, and controlling factors for medium-deep reservoirs forming and the high temperature and over pressured gas reservoir in the Dongfang area. It is found that the western provenance from Vietnam, the reservoir-cap assemblages and the lithological traps with certain reservoir physical properties of the upper Miocene submarine fan are the key controlling factors for the formation of high temperature and over pressured gas reservoirs. Large scale of natural gas exploration has not been launched so far for the medium-deep strata in the Ledong area. But the basic conditions for hydrocarbon accumulation remain similar between the deep and the shallow. Of course, there may be few differences in provenances, reservoirs and reservoir-cap assemblages between the two areas. However, the conditions of reservoir-cap assemblages and traps are even better in the deeper part according to newest information. In conclusion, there is great potential to discover medium and deep commercial high temperature and over pressured gas reservoirs in the medium-deep layers of the Ledong area.