A highly accurate U-Pb age of（132.5±2.4）Ma was obtained for zircon from the Laowan granite in Tongbai area by using the U-Pb SHRIMP method. It is concluded that the Laowan granite intruded during Middle Yanshanian rather than Late Yanshanian as some researchers have considered. Considering the timing of the regional tectonic-magmatic activity, the authors hold that there existed an important tectonic-magmatic event during Middle Yanshanian, with the Laowan granite being the product of this event.