Abstract: It is traditionally considered that shale gas reservoirs do not contain or contain little hydrogen sulfide (H₂S). However, low to extra-high content of H₂S has been detected in 9 shale gas reservoirs in the ten years of exploration and development practice, and high to extra-high content of H₂S are often found in calcareous shale gas reservoirs. According to the sequential order of H₂S formation time, "natural geological process" and "anthropogenic cause" are regarded as two major causes for the occurrence of H₂S in shale play. The former focuses on demonstrating the residue or migration of primary H₂S in gas reservoirs as a result of the natural geological processes, while the latter emphasizes that the introduction of microorganisms and chemical substances by field operations (such as drilling, hydraulic fracturing) can result in the formation and emergence of secondary H₂S after multiple processes under the complex downhole conditions. The proposal of "anthropogenic cause" has shed new light on the occurrence of H₂S in shale gas reservoirs, but has not received much attention till now. Meanwhile, the mutually exclusive and complementary relationships between "natural geological process" and "anthropogenic cause" have not yet been clarified. Furthermore, the research of evaluating the primary supply capacity of H₂S in shale gas reservoirs shall be carried out in the future. Meanwhile, it is required to deeply explore and establish the genesis identification criteria and output prediction system of epigenetic H₂S based on field production data, so as to deepen the understanding of the genetic mechanism of H₂S in shale gas reservoirs, thus providing a theoretical support for subsequent exploration and development of shale gas.