Abstract: Tongchang corphyry copper deposit, together with the Zhushahong and Fujiawu porphyry deposits, makes up Dexin copper field-the largest copper field in China．It is located in the northeast part of Jiangxi province, China．The ore bodies are mainly found in the contact zone between the Proterozoic Jiulin group and granodiorite porphyry body．This paper focuses on the oxygen isotope composition and variation pattern of the granodiorites in vertical direction, and their relation with the alteration of granodiorite in Tongchang porphyry copper deposit Dexin. The result show that the δ180 values of granodiorite, whole rock; vary from 6.4‰ to 10.7‰, and the feldspar separates have theδ18O value of 6.5‰ ～ 8.9％. There exits certain variation pattern for the oxygen isotope composition of the granodiorite whole rocks and feldspar, separates, namely, theδ18O values of the whale rocks and feldspar separates decrease with the depth from the surface to the deeper levels Through oxygen isotope exchange calculation between meteoric water andgranodiotite using Taylor’s model, it can be inferred that the meteoric water with a value of -8.5‰ circulated in the wall rocks of granodiorite firstly, and then continued to flow from deeper levels to the surface in mining area. Because of different interaction temperatures and δ18O values of the interacted water at the shallower and deeper positions, the granodiorite whole rocks have different variation patterns: the altered rocks of the shallower levels usually, have higherδ18O values, while the lowerδ18O values of the grannodiorites arc found in the deeper positions. The oxygen Isotope compositions and their variation pattern of quartz samples are different from those of whole rocks and feldspar separates. Theirδ18O values(8.4-9.8‰ )are not related to depth, but related to the extent of alteration. The quartz samples of intensely altered grannodiorties have the highest δ18O values The increment of quartz during alteration of feldspars is responsible for their oxygen isotope composition change. It can be inferred that the ore-forming fluids of Tongchang porphyry copper deposits were derived from the evolved meteoric water.