Elemental sulfur is widely dispersed in the hydrocarbon source rocks and its depositional environment is usually thought as a reducing environment. The presence or absence of free oxygen is a key to identify oxidizing or reducing environment. But elemental sulfur is often present as an oxidant in this environment. When elemental sulfur meets with organic matter, redox reaction will occur. In our simulation experiments at 200-400℃, the existence of elemental sulfur can sharply increase the amounts of hydrocarbons, hence leading to the production of immature or low-mature oils and natural gases. At the temperature of 300℃, the addition of elemental sulfur will further enhance the relative yields of hydrocarbons, and the final yield of total extracts and gaseous hydrocarbons of similitude kerogens by more than 463% and 2760%, respectively, while those of oil shales are increased by about 71% and 2044%, respectively. But at the temperature of 450℃, elemental sulfur plays a negative role in liquid hydrocarbon formation. The presence of elemental sulfur is probably a key factor in the gypsolyte environment leading to the formation of immature or low-mature oils, as well as the coexistence of immature or low-mature oils and natural gases. Elemental sulfur is unus dispersed in the hydrocarbon source rocks and its depositional environment is usually thought as a oxidizing environment. The presence or absence of free oxygen is a key to identify oxidizing or reducing environment. But elemental sulfur is often present as an oxidant in this When elemental sulfur meets with organic matter, redox reaction will occur. In our simulation experiments at 200-400 ° C, the existence of elemental sulfur can sharply increase increase of amounts of hydrocarbons, hence leading to the production of immature or low-mature oils and natural gases. At the temperature of 300 ° C, the addition of elemental sulfur will further enhance the relative yields of hydrocarbons, and the final yield of total extracts and gaseous hydrocarbons of similitude kerogens by more than 463% and 2760% respectively, while those of oil shales are increased by about 71% and 2044%, respectively. But at the temperature of 450 ° C, elemental sulfur plays a negative r ole in liquid hydrocarbon formation. The presence of elemental sulfur is probably a key factor in the gypsolyte environment leading to the formation of immature or low-mature oils, as well as the coexistence of immature or low-mature oils and natural gases.