Tin mineralization is extremely uneven distributed in the world, and is closely related to granitic magmatism, which attached considerable attention on the granite tin metallogenic capacity study. It is important to well constrain the magmatic source and accurately trace the magmatic evolution process for understanding the tin metallogenic capacity of granite. Apatite, as a common accessory mineral in granitoids, its chemical composition has a unique advantage in tracing the magmatic sources and diagenetic process of its host granite. In this study, apatite in situ chemical composition analysis of granite from the Xiaolonghe tin deposit in the TengchongLianghe tin belt in western Yunnan Province was carried out. The results show that the granite from the Xiaolonghe tin deposit is of highly differentiated granite, and characteristic of Atype granite. The granite magma is mainly originated from the ancient continental crust. The granite, with rich F and certain Cl content, was formed in a relatively reductive environment. These characteristics of the Xiaolonghe granite indicate that it is conducive to the accumulation and migration of Sn in the granitic magmatic evolution process. Thus, the structure and chemical composition of apatite can well constrain the granite genesis, magmatic evolution, physical and chemical conditions of magma, which can effectively evaluate the tin metallogenic capacity of granite.