The Mesozoic ground geology of Da Hinggan Mts. is studied in this work in combination with the structural features of the crust, upper mantal, and asthenosphere at various depths to reconstruct the geologic evolution of this area. The results reveal a two-stage orogenesis of the Da Hinggan Mts. : the first stage of contenantal-crust accretion starts from the Early Mesozoic underplating and goes through an extenssive crust-mantle magma intrusion and eruption until the Late Mesozoic, and the the second stage of upwellung is marked by formation of the basin-and-range structure in the Early Cretaceous. Upon such a special orogeny duscovered in Da Hinggan Mts. , a possible mechanism - extentional orogenesis - is proposed to explain some of the intracontenantal orogenes, and a preliminary understanding is obtained about their complucated features that are those of the plate-marginal orogenes.