Abstract: Yudongzi complex is the oldest geological mass in the Qinling area. Previous researchers have determined the age of Yudongzi Group in many ways, but the results are quite diverse, thus poor in accuracy. Based on image features of zircon, combined with genetic analysis of zircon and microdomains U-Pb isotope LA-ICP-MS (laser ablation ICP-MS) determination, separately we've obtained the magma crystallization age 2661±17Ma and 2703±26Ma respectively for mylonited fine-grained biotite granite and strong schistosity biotite granite in Yudongzi complex, and metamorphic zircon age 2647±65Ma in the mylonited fine-grained biotite granite. Among which 2703±26Ma is the oldest intrusion that had been discovcered in the Qinling Orogenic Belt up to now, it provides a new evidence for Precambrian tectonic-magmatic events and the evolution of early Earth in Qinling Orogenic Belt research.