The Dongshengmiao large-sized polymetallic pyrite deposit in Langshan area of Inuei Mongolia is located in the western part of northern North Ghina platform and occurs within Langshan-Zhaertai faulted trough. The ore-bearing rock series of Middle Froterozoic Langshan Group is a set of fine elastic rocks- carbonate rocks which have undergone epimetamorphism. This ore deposit bears resemblance to gigantic Proterozoic pyrite type deposits, in the world in many aspects .In this paper, the author has made a special discussion on the major ore mineral in the deposit-sphalerite, looking into the relationship between the typomorphic characterstics of sphalerite and genesis of the ore deposit. Sphalerite of this deposit was formed irr two stages, with the early sphale- rite related to submarine hot-water exhaled deposition whexeas the late spha- lerite to late stage regional metamorphism, being the product of local mobiliza- tion, accumulation and recrystallization. The author has further investigated the formation conditions of sphalerite .FeS molecules in sphalerite increase obviously from early stage to late, and the Zn/Fe ratio decreases from 8.64 to 4.06.The unit cell parameter of sphalerite grows with the increasing FeS content. Co content gradually decreases from early to late stage.Temperature for the for- mation of sphalerite tends to rise from early to late.Sphalerite formed in the process of late metamorphic transformation contains more iron than the originally sedimentogenicsp halerite, thus constituting a mineral sequence from sphalerite to marmatite. Typomorphic characteristics of sphalerite indicate undoubtedly that the Dongshengmiao pdlymetallic pyrite deposit is genetically of submarine hot-water exhaled deposition-weak reformation type.