Abstract: Based on the deep researches of diagenesis in the northwestern Sichuan,chemical composition of the fluid inclusions in different formations and different attitudes were analysed by Laser Roman Microspectrometer.And the distribution characteristics of H₂S and its migration features were discussed.The results show that the charging of hydrocarbon with high H₂S concentration from low formation last a long time.Hydrocarbon being charged at the stage of diagenesis of the 2nd Member of Xujiahe Formation has a high H₂S concentration and its migration pathway are mainly the hole,throat and fissure system,while hydrocarbon being charged at the later stage has a relatively low H₂S content and its migration pathway is mainly the fissure system.And sustained reducing environment is necessary for H₂S not being exhausted during migration.