Abstract: Yuantoushan is located in the north of Tailuko belt, eastern Taiwan. It is mainly composed of strongly deformed and metamorphosed granodiorite-gabbro "slurry mixed rock" combination. Deformed intrusions are in the center and show typical magmatic features, representing magmatic events after deformation and metamorphism. The authors carried out field geological survey and petrologic as well as isotopic geochronologic studies of metamorphic intrusive rocks and intrusive rocks. It is shown that there are significant differences in rock characteristics and main trace elements between the two kinds of rocks, indicating that the two kinds of rocks are products of different tectonic magmatic events. Undeformed intrusive rock is quartz diorite, with high Pb, Rb, U, Th, Zr, exhibiting mild enrichment characteristics of I type granite, and its LA-ICP-MS zircon U-Pb isotopic age is 82 ±1Ma, suggesting the Late Cretaceous Campanian period. This indicates that the deformation and metamorphism event in eastern Taiwan were ended, and the evolution then entered a non-squeezing neotectonic stage.