The Dayinhe intrusion, located in the northwest of the Xiao Hinggan Mountains, is mainly composed of alkali-feldspar granite and syenogranite. Zircon U-Pb age obtained by LA-ICP-MS analysis of the alkali-feldspar granite is 304.4±1.3 Ma, suggesting that it intruded in the Late Carboniferous period rather than the Late Jurassic period as proposed before. Petrochemically, the Dayinhe intrusion is characterized by high Si, Na, K and low Ca. It is enriched in Rb, La, Th and depleted in Ba, Sr. Nb, Ta, Zr, implying the effect of plagioclase as the stable residual phase in the magma source. Regionally, the Dayinhe intrusion, together with the Shierzhan, Xinkailin, Longzhen and Zhalantun granites that share the same petrologic and geochemical characteristics, forms the Late Carboniferous post-orogenic I-type and A-type granite belt in the Da Hinggan Mountains, implying the end of the collision and orogen between the Hinggan block and the Songnen block and the beginning of post-orogeic extension in this region.