Abstract：Lots of evidence shows that magma mingling existed in the Jiama ore deposit. It is of great geological significance to study the magma mingling. Based on tectonic and magmaic theory, this paper has established tectonic and magmaic 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 underplating 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 (mafic magma) and 60% acid end-member (granodioritic gneiss) , 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, inmplying that the mingling of magma contributed to mineralization.