Abstract: By applying the theory of metallogenic sequence, the law of ore-forming element association and some metallogenic models in association with existing data, it has been verified that there might exist a tin-bearing polymetallic ore field （hidden） between Dadong and Longkou, western Yunnan. As is known now, in the area there are the Dadong leadzinc deposit （bearing tin） in the north and the Longkou tiniron deposit in the south, between which there are several mineralization occurrences of copper, aluminium and zinc. In the area, the ore-forming elements exhibit distinct zoning, and Cu, Pb, Zn and Sn often form a paragenetic association. According to these geochemical characteristics and analysis of ore-source material, it is fully, demonstrated that the present mineral deposits （occurrences） only represent the outer zone of the vertical zoning of this metallogenic district, while at depth there might occur tin mineralization of Gejiu type. Tin mineralization of western Yunnan mainly occurs along the endo-and exo-contact zones of the Yanshanian granite. According to this general regu- larity combined with an analysis of the characteristics of the geological structure in the area, it is inferred that there exists a hidden rock body, which is the important condition for the formation of a hidden ore field. A summarization of the various main characteristics and comparison with some important tin ore districts both inside and ouside the province all implies the possibility that a hidden tin-bearing （or tin-dominant） polymetallic ore field was formed in the area. For this reason, the author suggests that an in-depth study should be made in this area, which may help to enlarge the tin resources of western Yunnan, and then it is necessary to summarize practical expexience in order to open a new realm for ore prospecting.