Abstract: The Demohada volcanic-eruption basin is one of the most important Late Mesozoic volcanic basins in southern Da Hinggan Mountains. It is considered that the Demohada volcanic-eruption basin is composed of volcanic rocks of Baiyin'gaolao Formation, which is divided into three lithologic segments and constitutes a total sedimentary and eruption cycle. The volcanic rocks have eight types with nine Ⅴ-grade volcanic apparatuses, obviously controlled by NNE-trending faults. The results of zircon U-Pb dating show that the volcanic activity of the basin occurred mostly from 128Ma to 125Ma, suggesting Early Cretaceous.