Laoyaquan alkali granite complex and such bodies as alkali-rich small granite porphyry pluton, greisen-type tin ore body and quartzite tin ore body that have intruded the alkali granite possess similar REE distribution patterns. They all show strong depletion of Eu, and their trace element spidergrams and other geochemical characteristics are similar too. Therefore, the phenomena that crustal constituents contaminated alkaline magma at the late stage of the fractional crystallization and the magma evolved in the acidic direction might have constituted one of the important prerequisite for alkali granite mineralization in the tin deposit.