Abstract: The theory of (large) ore deposit forming in the small intrusion is an important result of decades of prospecting practice by academician Tang Zhongli. The theory started from magmatic copper-nickel sulfide deposits, gradually extended to hydrothermal deposits associated with intermediate-acid magmatism, and developed into a complete metallogenic theoretical system of basic-ultra-basic and intermediate-acid magmatism in parallel. In recent years, it has been found that the metallogenic belt represented by the Mian-Luo-Ning ore concentration area is distributed in many superimposed areas of basic-ultra-basic and intermediate-acid magmatic activities, among which the formation process of the Jianchaling cobalt-nickel-gold polymetallic deposit experienced the preliminary ultramafic magmatic liquation in the earlier stage to achieve the pre-enrichment of ore-forming elements, and the later superimposed acid magmatic fluid on eventually led to both cobalt-nickel and gold mines reaching large scale. In recent years, the Hejiaya cobalt-nickel deposit was found in the Baiqisi basic complex also has the characteristics of superimposed mineralization of two kinds of magmatism, which provides a new research direction for the theory of (large) ore deposit forming in the small intrusion. At present, the new round of prospecting breakthrough action has been fully launched. The strategic key metal minerals represented by Co and Ni are still the top priority of the prospecting work. The superposition of small rock bodies is an important geological process in the formation of Co and Ni ores. In this paper, the development process of the theory of (large) ore deposit forming in the small intrusion is introduced, and the basic connotation of the superimposition of two kinds of magmas into (large) ore is put forward by taking the Mian-Lue-Ning ore concentration area as the representative. On this basis, the prospect of prospecting application and theoretical research is made, which is expected to support the new round of prospecting breakthrough action.