Abstract: On the basis of geological and geochemical characteristics of the Yinshan polymetallic deposit, Jiangxi province, and from the view point of water-rock interaction and related isotope exchange, the present paper queries the validity of the conclusion that magmatic water was the main origin of ore-forming fluid in Yinshan deposit, which was proposed by some previous studies. Oxygen isotope compositions of altered rocks and fluid were determined for reverse calculation of water-rock isotope exchange. It shows that the ore fluid of Yinshan deposit was originated from meteoric water instead of magmatic one. This fluid was the product of interaction between the down going meteoric water and phyllitic wall rocks which had higher a δ18O values in deeper portion at higher temperature (≥ 400℃) and lower W／R ratio (≤ 0.05). As a result, the δ18O value of the fluid had been greatly enhanced and could reach the value similar to mgmatic water, which is easy to lead to the conclusion of a magmatic origin. As a matter of fact, the small-some subvolcanic magmatism in Yinshan area mainly served as a heat source but not a water source for the large-size mineralization.