The magma thermal field is an instantaneous thermal field in a very short period of time and in a local region caused by magma, which makes geothermal gradient obviously high. The scale of the magma thermal field is small, usually a few meters to several kilometers away from intrusions. The scope, scale and shape of the magma thermal field is related to temperature, composition, shape, size, depth of the intrusion, and fluid, structure, properties of surrounding rock and so on. The magma thermal field is a place where fluids rise. It is an important difference which makes the magma thermal field is different from the geothermal field that the magma thermal field often accompanied by fluid activity, is a place of fluids circulation, rise and absorbing useful metal elements in the crust. This paper discussed the relationship between the magma thermal field and polymetallic hydrothermal mineralization, and the role of magma thermal field in the magmatic hydrothermal deposit, hydrothermal sedimentary deposit, hot spring deposit and metamorphic hydrothermal deposit. It explains the mineralization from a new perspective. It may explain many difficult and controversial issues, such as the problem of multiple sources, metals and causes, why gold-copper deposits and tungsten-tin deposits can be associated, why some granites related to mineralization but others are not, why mineralization lag behind of granite, the genesis of Calin-type gold deposit, the problem of some stratabound SEDEX type and MVT type Pb-Zn deposit reenrichment, why some skarn is away from the intrusion, and so on. This paper indicates the reasons why large-scale magmatic activity and large-scale mineralization is closely related. It makes magma thermal field from an open system into a closed system in a local scope. In this closed system, the temperature of the surrounding rock can achieve higher, heat can last longer. It promotes the fluid convection circulation in the range of this magma thermal field, makes the fluid can draw useful metal element as much as possible from the surrounding rock with incomparable effect. Many large super-large polymetallic deposits may be associated with this kind of mineralization. From the angle of the magma thermal field, metallogenic potentiality of large-scale magmatic activity is virtually unlimited. This paper also discussed existing problems about principles and applications of the magmatic thermal field, and pointed out that the relationship between the magma thermal field and mineralization is notable. It may be able to change our current deep-rooted understanding of metallogeny, carved out a new field, advanced deposit studies into a new stage.