H

2

S in natural gas can be produced by biochemical process

thermochemicalprocess or magmatism. The decomposition of sulphur-bearing organic matter andthe reduction of sulfate in higher temperature are the main geneses of H

2

S. Si-mulating test made by the authors indicates that sulfate can produce H

2

S inhigher temperature. Some evidences found in rock samples show that carbonateand pyrite replaced anhydrite and formed H

2

S. It is predicted that natural gasat the depth of 3600-6600m in the Jiyang Depression has the highest contentor H

2

S.