A series of volcanic rocks, such as basalt, andesite and rhyolite, were determined in Xin Barag Right Banner of northern Da Hinggan Mountains. Geological survey reveals that these volcanic rocks should be assigned to Hadataolegai Formation. SHRIMP zircon U-Pb dating indicates that the epidotized andesite from Hadataolegai Formation was formed at(254.3±7.9)Ma(MSWD=4.7). According to geochemical researches, these volcanic rocks of Hadataolegai Formation can be divided into two types, i.e., intermediate-basic rocks and acidic rocks. The magma of intermediate-basic rocks was derived from the lithospheric mantle affected by the southward subduction of Mongolia-Okhotsk plate. The acidic volcanic rocks have a crustal-derived magma source features. Based on tectonic setting analysis, the authors hold that the Hadataolegai Formation volcanic rocks were formed under the continental marginal arc environment and related to southward subduction of Mongolia-Okhotsk plate. The determination of Hadataolgegai Formation improves the stratigraphic sequence of northern Da Hinggan Mountains and provides a favorable evidence for regional tectonic evolution of Da Hinggan Mountains.