The Meixian granitic pluton is located in the southwest of Mufushan granitic batholith. Its diagenetic age and petrogenesis are of great significance to study of the genesis of Neoproterozoic granite belt and its tectonic background in northeast Hunan. In this study, LA- ICP- MS zircon U- Pb dating, zircon Hf isotope, and whole- rock geochemistry were carried out for medium- coarse- grained and fine- grained biotite granites from the Meixian pluton. The analysis results show that the ages of medium- coarse- grained and fine- grained granites are 819.6±4.6 Ma and 810.4±4.7 Ma, respectively. Thus, it is confirmed that the Meixian pluton was formed in the Neoproterozoic and represent the end of the Neoproterozoic tectono- magmatic activities peak in the middle of the Jiangnan Orogen. The Meixian medium- coarse- grained granite has εHf (t)=5.4~10.1, tDM=1.31~1.04 Ga, and the fine- grained granite has εHf (t)=5. 0~9. 9, tDM2=1.33~1.06 Ga. The Meixian granites have positive εHf (t) values, and its Hf two- stage model ages are close to the peak values of Hf two- stage model ages (1.4~1.0 Ga) of clastic zircons in the Lengjiaxi group, suggesting that its parent magma has the involvement of new crustal materials. In terms of geochemical composition, The Meixian granites are characterized by silica- alumina- rich, high sodium, medium- low potassium, weak peraluminosity, more enriched in Rb, Th, U, Li and LREE, deficient in Ba, Nb, Sr and Sm, and complex Eu anomalies (δEu=0.58~1.61), belonging to or similar to volcanic arc granites. The Mg#values of the Meixian granites (45~59) are significantly higher than those of crustal melt (17~38), suggesting that their parent magma may be mixed with a certain proportion of mantle- derived materials. Combined with previous studies, this paper suggests that the Meixian granites should be atypical I- and I- S- type granites formed by partial melting of the neogenic igneous crust caused by the underplating of mantle- derived magma. They were formed at the late stage of continental collision between the Yangtze and Cathaysia blocks, and the special period when the tectonic background of the Jiangnan Orogen was transformed from compression to extension.