Laochang ore field of Gejiu, as a famous tin-copper polymetallic ore producing area in China has received great attention. The paper aimed at the granite in the ore field, and mainly studied geochemical characteristics of the granite, source area and tectonic settings. Combined with the geological background and lithological features of the granite body, the research indicated that the Laochang granite is a compound massif, resulted from partial melting of the crust rock, and of the features of different source area. The diagram of tectonic discrimination shows that different granite units of the Laochang compound massif formed at different structural environments and the granite related to metallogenesis formed at the transitional stage from the post-collisional orogeny to intraplate environment, which is most favorable condition for the formation of super-large deposit in the Laochang ore field.