Pollen analysis and ¹⁴C dating of Chichi peat marsh in Betula ermanii forest, the Changbai Mountains show that the peat deposit of the marsh probably accumulated after 3400aB. P. There might be vegetation succesion between dark coniferous forest and Betula ermanii forest there since then. The palaeoclimate estimated from major factor anal-ysis of pollen data reveals that the climate had begun to descent before 3400aB. P. It was a relative warm period between 3400-2200aB. P. Then the climate declined rapidly and reached the lowest level in 1800aB. P. Later,it changed alternatively in warm and cool. The comparatively warm periods were respectively 1200,800 and 200aB. P.,and relative cool periods 1000 and 400aB. P.