Abstract：Many Au (Ag)-polymetallic ore deposits have been discovered in the volcanic rock series of the Xiong’er Group on the south margin of the North China plate. However, there are many different explainations for the genetic mechanism of these deposits. Based on a systematic study of the geological characteristics of these deposits, features and genesis of hydrothermal ore fluids, mineralized and alterated host rocks, the authors propose the new views that the volcanic hydrothermal fluids after the Xiong’er volcanic activity is the main factor controlling the formation of the Au (Ag)-polymetallic ore deposits, and that the major ore-forming processes are depostion and cavity filling of hydrothermal fluids. In addition, the authors also suggest that the main mineralization stage is the late phase of the Xiong’er volcanic activity.