Abstract: LA-ICP-MS zircon U-Pb geochronologic study and whole-rock geochemical analysis were undertaken for the monzonitic granite in Yilehuli Mountain area in northern Da Hinggan Mountains, with the aim of constraining its formation time, petrogenesis and the regional tectonic setting. Dating data show that monzonitic granite formed at 158.1 ±0.7 Ma before the Late Jurassicearly magmatic evolution event. The geochemical studies show that the granite in the area has the characteristics of high Si, Na, K and Al and low Fe and Mg, with A/CNK being 0.83~1.09, thus belonging to high potassium calc alkaline granite; it is enriched in the large ion lithophile elements K, Rb, and depleted in high field strength elements Hf, Th; the total REE is higher, and the rare earth distribution curve is right-inclined, with weak negative Eu anomalies. According to these characteristics, the monzonitic granite should belong to type I granite. The magma originated from the rock melting of the of the basaltic components of the lower crust, being the product of the thickening process with the crust during the collision. The formation of the early Late Jurassic monzonitic granites in the study area were related to the continental-continental collision environment in the closure process of the Mongolian-Okhotsk suture zone, and the closing time of the Mongolia Okhotsk Ocean in North Da Hinggan Mountain-Yilehuli mountain area is also confined to early Late Jurassic.