Abstract: The magnesite deposit in Liaoning Province, tectonically located in the southeast margin of the MesoNeoproterozoic Fanhe rift and the north margin of Archean Fushun-Qingyuan craton, is composed of four individual ore bodies trending east-west, among which the Tongjiajie orebody is the largest. The deposit occurs in the aplite-dolomite of the 4th member of Gaoyuzhuang formation, Changcheng system, Mesoproterozoic. In the geological survey to the Tongjiajie magnesite deposit, the metallogenic background and geologic characteristics of the orebody, as well as the ancient sea water, paleoclimate and paleogeography, are studied and analyzed. The genesis of the deposit is considered to be of sedimentation, with the reformation by metamorphic recrystallization and metamorphic hydrothermal fluid.