The Toudaohe pluton, located in Mingshui area of middle Da Hinggan Mountains, is mainly composed of granodiorite and monzogranite. LA-ICP-MS zircon U-Pb data indicate that the Toudaohe pluton formed during the Middle Triassic with the ages of 243～240 Ma. Geochemically, the granitic rocks are high in SiO₂ (61.32%～78.19%), and Al₂O₃ (11.85%～16.87%), but low in total Fe₂O₃ (0.56%～5.93%), MgO (0.16%～3.30%), and CaO (0.26%～2.94%), suggesting that they are high-K calc-alkaline I-type granites. These granitoids have low total REE content (ΣREE=75.5×10^-6～149.49×10^-6) with fractionated REE , and no remarkable Eu anomalies. Moreover, they are enriched in large ion lithophile elements (e.g., Rb, Pb, Th, U), and depleted in high field strength elements (e.g., Nb, Ta, Ti). Zircon Hf isotope analyses show that these granitoids have high initial ¹⁷⁶Hf/¹⁷⁷Hf ratios (0.282 811～0.283 227), positive εHf(t) values (6.55～21.28), and young Hf two-stage model ages of 595～1 107 Ma. These geochemical characteristics indicate that the source materials of Toudaohe pluton were juvenile igneous crust rocks which originated from depleted mantle during the Mesoproterozoic to Phanerozoic period. Based on regional geological investigations and spatial and temporal distribution of the coeval igneous materials, the authors hold that the Middle Triassic Toudaohe pluton was emplaced in a post-orogenic extensional environment linked with the final closure of the Paleo-Asian Ocean.