The Mesozoic volcanic rocks in the Da Hinggan Mts.and its adjacent area s were formed in two backgrounds,divided by an important geological event, i.e. the Tuc hengzi orogenic movement(156～145 Ma);therefore the volcanic rocks, which were formedbefore and after the movement,could not be compared in characteristics of evolution or space distribution.According to the study in tectonics,tectonost r atigraphy, palaeomagnetism and geophysics,the early stage of the late Jurassic （156～1 45 Ma）is the strong orogenic period of the Da Hinggan Mts.,i.e.the Da Hinggan Mts.were in the backgroung of strong compression.It was in this period that th e Da Hinggan orogenic belt was formed,which is socalled the Tuchengzi orogeni c movement(156～145 Ma).According to the result of geochemical analysis the vol canic rocks of the late Jurussic to early Cretacous（150～100 Ma）were formed in the compressional background.Comprehensive study shows that the volcanic ro cks of the late Jurussic to early Cretacous（150～100 Ma）were formed in the com pressional background of postorogeny with a "reduced pressureshearing" proc e ss.Besides the volcanic rocks of this age are very different from those of mantl e plume.