Abstract: De'erni copper deposit, located in the southern slope of De'erni, in the middle of Jishi Mountain, Maqin country, Qinghai Province, is a comprehensive utilization deposit which is dominated by copper. Because there are considerable differences in its ore-genesis, we have studied its ore-genesis by macro-observation, mineralogical studies and electron probe analysis in detail. This is the first time that barite and gypsum were discovered. Quartz-carbonate-barite-gypsum is not only a low-temperature mineral assemblage but also is a typical mineral composition of submarine hydrothermal deposit. By mineral environment of structure, material source, strawberry-like structure, siliceous rockslying at the top of the orebodies, the discovery of barite and gypsum, we suggest that De'erni copper deposit is hydrothermal exhalative-sedimentary deposit in seafloor.