Based on results of microscopic observation and laser Raman analysis about fluid in- clusions, multiple special forms of immiscible inclusions that contain sulphur, liquid hydrocarbon, bi- tumen, etc. were discovered in samples collected from the H2S gas reservoir-containing carbonates in the Lower Triassic Feixianguan Formation in the Jinzhu-Luojia area, Kai County, Sichuan Province. Based on the lithology and burial history of the strata involved as well as measurement results of homogenization temperature of fluid inclusions, bitumen reflectivity, etc., it is concluded that the H2S in the gas reservoir resulted from the thermal reaction between hydrocarbons in reservoir and CaSO4 in the gypsum-bearing dolostone section at the high temperature (140℃―170℃) oil-cracked gas for- mation stage in Late Cretaceous. Thereafter, research on a great number of immiscible inclusions in the reservoir reveals that elemental sulphur resulted from oxidation of part of the earlier-formed H2S and further reaction between sulphates, hydrocarbons and H2S in geological fluids in H2S-bearing gas reservoir at a temperature of 86℃―89℃ and a pressure of 340×105Pa and during the regional uplift stage as characterized by temperature decrease and pressure decrease in Tertiary. Meanwhile, gyp- sum, anhydrite and calcite formed at this stage would trap particles like elemental sulphur and result in a variety of special forms of immiscible inclusions, and these inclusions would contain information concerning the complexity of the fluids in the reservoir and the origin of H2S and natural sulphur in the gas reservoir. Based on results of microscopic observation and laser Raman analysis about fluid in- clusions, multiple special forms of immiscible inclusions that contain sulfur, liquid hydrocarbons, bi-tumen, etc. were discovered in samples collected from the H2S gas reservoir-containing carbonates in the Based on the lithology and burial history of the strata involved as well as measurement as a homogenization temperature of fluid inclusions, bitumen reflectivity, etc., it, is is that that Lower Triassic Feixianguan Formation in the Jinzhu-Luojia area, Kai County, Sichuan Province. the H2S in the gas reservoir resulted from the thermal reaction between hydrocarbons in reservoir and CaSO4 in the gypsum-bearing dolostone section at the high temperature (140 ℃ -170 ℃) Oil-cracked gas for- mation stage in Late Cretaceous. on a great number of immiscible inclusions in the reservoir reveals that elemental sulfur resulted in oxidation of part of the earlier-formed H2S an d further reaction between sulphates, hydrocarbons and H2S in geological fluids in H2S-bearing gas reservoir at a temperature of 86-89 ° C and a pressure of 340x105 Pa and during the regional uplift stage as characterized by temperature decrease and pressure decrease in Tertiary ., Gyp- sum, anhydrite and calcite formed at this stage would trap particles like elemental sulfur and result in a variety of special forms of immiscible inclusions, and these inclusions would contain information concerning the complexity of the fluids in the reservoir and the origin of H2S and natural sulfur in the gas reservoir.