Based on tectonic and magmatic theory, this paper has established tectonic and magmatic evolutionary sequence of the Jiama ore deposit in the Gandise metallogenic belt according to structural association features and genesis of the granitoids. It is held that underplaying was the direct power in the process of magma mingling, the original mechanism of mixed magma might have been the pre-mingling and emplacement that occurred at 15 Ma 40% basic end-member and 60% acid end-member, and the re-mingling of magma happened again along with mechanical mixture. The metal elements and S in ore-forming fluid came from mantle-derived mafic magma, implying that the mingling of magma contributed to mineralization.