The Dexing porphyry copper deposit, Jiangxi Province, is the largest porphyry copper deposit in eastern China. Previous studies indicated that the ore-forming fluids were dominantly derived from the magmatic system, plus additional meteoric water, but there have been some controversies on the petrogenesis of the ore- bearing porphyries and the tectonic setting and ore-forming source of this deposit. Our new studies have suggested that the Dexing porphyries were emplaced in a continental arc setting coupled with the westward subduction of the Palaeo-Pacifie plate in the early Middle Jurassic (170.2 -171.0 Ma). Partial melting of the subducted slab (mainly overlying sediments), with subsequent melts interacting with the lithospheric mantle wedge, formed the high-K calc-alkaline porphyry magmas with high St, Sr/Y and La/Yb affinities. The large scale Cu--Mo--Au mineralization was nearly contemporaneous with the magmatism, and the ore-forming source were extracted from the Fe3+ -rich fluids/magmas released by the P-MORB interacting with the lithospheric mantle wedge. However, during the middle Late Jurassic( - 153.5 Ma), Dexing area had been converted to a back-arc or an intra-arc extension environment triggered by the rollback of the palaeo-Pacifie plate, and there formed the ore-barren dioritic intrusions with a crust--mantle mixing source. Moreover, there had formed a hydrothermal Cu (Au?) metallogenie event superimposed on the porphyry Cu--Mo--Au mineralization during the late Early Cretaceous.