The Huojihe molybdenum deposit in the Xiao Hinggan metallogenic belt is a large porphyry deposit discovered in recent years. Based on the analysis of characteristics of mineralization, the authors conducted the LA-ICP-MS U-Pb dating of zircon from metallogenic granitic complex and Re-Os dating of molybdenite in Huojihe area. LA-ICP-MS U-Pb ages of zircons from medium-fine grained granodiorite and porphyritic granite are 181.0±1.9 Ma (n=15, MSWD=4.7) and 193.6±1.4 Ma respectively. The molybdenite Re-Os isochrones age is 176.3±5.1 Ma (n=6, MSWD=1.3), with weighted average model age of 181.2±1.8 Ma. The ages from the two methods are close to each other, suggesting that they might have been formed in the same petrogenetic ore-forming system. The petrogenesis started at 193.6±1.4 Ma and the mineralization in the magma occurred at 181.2±1.8 Ma. The ore-forming age of the Huojihe molybdenum deposit is close to the molybdenite Re-Os isochron age of the Wunugetu Cu-Mo deposit and the Lanjiagou and Yangjiazhangzi molybdenum deposits. There existed an early Jurassic magmatic-mineralization event in Northeast China. Trace element and isotope show that granodiorite and porphyritic granite in Huojihe belong to A-type granites. Petrogenesis and mineralization of Huojihe molybdenum deposit were related to changes of the tectonic environment from crust extruding to extending. The mineral source was derived from magma.