Early Carboniferous arc volcanic rocks lie in Hongyan area of northwestern Xiao Hinggan Mountains. The volcanic rocks consist of basalt, andesite, dacite and rhyolite. Petrological and geochemical studies indicate that the volcanic rocks are of typical calc-alkaline type and display relatively high-K features. They are enriched in LREE (LREE/HREE=4.19～13.83) and LILE (Rb, Ba, Th and U) with obvious depletion of Nb,Ta and Ti, which suggests an active continental margin environment. The authors hold that the volcanic rocks of Hongyan area were derived from partial melting of enriched lithosphere mantle and experienced mainly crystallization differentiation with a small extent of lower crust assimilation(AFC-type processes). In combination with regional structures and geochemistry of volcanic rocks, it is concluded that the Early Carboniferous volcanic rocks of Hongyan area were probably formed in a pre-collision subduction environment and might have been related to the collision and collage between Erguna-Xingan and Songnen blocks.