In order to explore the petrogenesis of quartz diorite porphyry and the ore-forming contribution of mantle-derived basic magma, this paper present LA-ICP-MS zircon U-Pb dating, Hf isotope and whole rock geochemical study for quartz diorite porphyries from Dexing porphyry Cu deposit. The LA-ICP-MS zircon U-Pb age of quartz diorite porphyries obtained is 169 Ma, in accordance with that of ore-forming granodiorite porphyries, indicating that they were emplaced during the middle Jurassic. The quartz diorite porphyries are characterized by low SiO₂ (58.41%~63.12%), K₂O (1.68%~2.94%) contents and A/CNK values(0.85~1.04), belonging to the calc-alkaline to high-potassium calc-alkaline rocks. They are enriched in large ion lithophile elements and light rare earth elements but depleted in high field strength elements Nb, Ta, Ti, and heavy rare earth elements. The Hf isotope composition of zircon with relative depletion, εHf(t)=2.20~7.93 (maximum 7.93), indicating that they were crystallized from lithospheric mantle-derived magmas. The zircon REE distribution pattern diagram shows an obvious positive Ce anomaly, and the magmatic oxygen fugacity (lg f_O2) varies from-20.05 to -6.66, reaching the magnetite to hematite oxygen fugacity buffer, indicating that they were crystallized from magma with high oxygen fugacity. Geochemical results show that quartz diorite porphyries, granodiorite porphyries (and the enclosed enclaves) conform to the evolution trend of magma mixing, which indicates that the ore-forming granodiorite porphyry may be the product of large-scale mixing of mantle-derived basic magma and crust-derived acidic magma in the Middle Jurassic, and the quartz diorite porphyry represents the mantle-derived basic end member in the process of magma mixing. Combined with previous research results, it is believed that quartz diorite porphyries in the Dexing deposit were generated by melting of subduction-modified lithospheric mantle, which was triggered by upwelling of the asthenospheric mantle related to the extensional setting during the middle Jurassic in South China. Underplating of the mantle-derived basic magmas could have provided heat for melting of the lower crust and subsequently mixed with the crust-derived acidic magmas, which generated the parent magmas of ore-forming granodiorite porphyries. In addition, the magmatic system of quartz diorite porphyry was highly oxidized, which was favorable for preventing the early sulfide saturation and contributing volatiles and metals to the Dexing ore-forming systems.