Abstract: In this paper, the geochemical characteristics and genesis of Guanyinhe granite vein in Hanyin County, Shaanxi Province have been discussed. The granite veinis located in the north of Mianlue suture,serving as one part of Baishuijiang-Baihe fold beam. Studies have shown that the lithology of this granite vein is granodiorite. It has high Si and Al contents, with low Fe and Mg contents, belongs to peraluminous calc-alkaline rock, which isrich in Rb, Ba, Th and other large ion lithophile elements, as well as Sr and other incompatible elements, with a low content of K, Ta and Nb elements, without Eu anomaly.REE pattern shows steep deviation. Photos under microscope show that calcite mineral has 2 forms, the ones are independent particles, the others are mineral scaused by plagioclase's erosion, indicating hydrothermal activity.Diagenetic type of this granite vein is I-type. Its tectonic environment is the ones of volcanic arc granite (VAG), which is close to the ones of syn-collision granite (syn-COLG), indicating that the granite vein was formed during the plate subduction and collision orogenic process in Late Permian and Mid-Late Triassic, and serving as the products of late magma hydrothermal.