The Himalayan orogenic belt, caused by the subduction and collision between Indian plate and Eurasian plate, is the youngest and largest currently active orogenic belt in the world. The LA-ICP-MS U-Pb zircon age of 515.5±2.3 Ma from the gneissic biotite granodiorite that intruded into the Namche Barwa complex in eastern syntaxis of the Himalayan orogenic belt provides a geological record of Pan-African tectonic-magmatic event in this area. The SiO₂ content is 66.47%～72.42%, the average of the A/CNK indexes is 1.03 (0.98～1.03), and all samples fall into the peraluminous region in the A/NK-A/CNK index diagram. The Rittmann index σ is between 1.53 and 3.08, belonging to the calc-alkaline series. Most of the samples fall into a high-K calc-alkaline series area in the SiO₂-K₂O diagram. The values of TiO₂, MgO, FeO^T, MnO and K₂O show a good linear relationship with SiO₂ content in the Harker diagrams. The chondrite-nomalized REE patterns indicate that the samples are enriched in LREE, (La/Yb)_N values are 19.1～63.8, with slightly negative Eu anomalies (δEu=0.62～0.79). Trace elements show the depletion of Ba, Nb, Ta, Sr and Z as well as the relative enrichment of Rb, Th and U. The negative εNd(t) values(-8.67～-10.57) and Nd model ages (t_DM=1.84～3.42) of the gneissic biotite granodiorite of Tanya Township indicate that this rock had an old upper crust material source. Combined with the initial ⁸⁷Sr/⁸⁶Sr ratio features, the authors hold that the source rock of the gneissic biotite granodiorite of Tanya Township was granitic magma that partially melted in a high temperature environment. From the tectonic environment discrimination diagrams, it is inferred that metaluminous-weakly peraluminous gneissic biotite granodiorite of Tanya Township was formed in the post-collisional stage characterized by the conversion from a compressional environment to an extensional. Combined with the isotope age 513 Ma,the authors consider that the Pan-African collisional orogenic movement in the eastern Himalayan syntaxis ended and started the post-collisional tectonic evolution in Early Cambrian period.