Abstract: We have researched the forming condition of gas hydrate in the South China Sea according to the physical oceanography, palaeo-climate, sedimentary environment,, and tectonic environment. The researching results show that there are different forming condition of gas hydrate in South China Sea. In the northeast part of the South China Sea the high salinity water has flowed from Philippine Sea, therefore, the organism producibility was higher and there have rich organic materials in sediments of the periods of oxygen-isotope 2, 4, 6. In these periods the sedimentary velocity was very high, so there are good material condition for formation of gas hydrate. In addition, from the end of Miocene to present, the Philippine Sea plate has collided with Asian plate in Taiwan area and extruded the northeast part of the South China Sea. As the extruding force in the sediments the fluid is very active and this is very good for the formation of gas hydrate. Therefore, we believe that there should be rich gas hydrate in the northeast slope of the South China Sea.