Plagiogranite is firstly found in the ophiolite in GuoganjianianMountain. Based on the study of field geological characteristics, petrology, geochemistry and isotope geochronology, the authors suggest the plagiogranite has similar characteristics of adakite, which is high in Al2O3(14.84%~15.35%); Sr(338×10-6~356×10-6); Sr/Y(Sr/Y=46.94~55.45) and low in Y, Yb(Y=6.42×10-6~7.20× 10-6, Yb=0.56×10-6~0.63×10-6). Zircon SHRIMP U-Pb dating age is (348±9) Ma and it represents the subduction time of oceanic crust. The above geochemical characteristics indicate that plagiogranite in the GuoganjianianMountain is the product of direct partial melting of subduction plate in high pressure, and these granites are likely produced in the environment of subduction zone.