Abstract: Laguocuo ophiolite is one of the most complete ophiolite combinations in the Shiquanhe-Yongzhu-Jiali ophiolitic belt, and has great significance for restoring the evolution of the oceanic basin. However, the studies of the Laguocuo ophiolite are poor, resulting in the unclear genesis and controversial age. In this paper, the authors conducted field survey, profile measurement, geochemical survey, LA-ICP-MS zircon U-Pb dating and Lu-Hf isotope analysis on the plagioclase granite and gabbro cumulates of the Laguocuo ophiolite so as to study the tectonic property of the Laguocuo ophiolite. Plagioclase granite and gabbro cumulate of Laguocuo ophiolite exhibit direct contact in the field, and their geochemistry data show that they are of the same source with similar REE patterns that are similar to features of the E-MORB. Lu-Hf isotope analysis shows that their magmatic source is the depleted mantle, and shows a plurality of components, which might have resulted from the mixing of DM and EM2. Zircon LA-ICP-MS UPb dating yielded concordia ages of 184.1±0.79Ma and 183.5±2.2Ma. The authors have reached the conclusion that Laguocuo ophiolite was formed in a back-arc ocean basin with strong MORB characteristics.