By using the forest gap model-FAREAST,we simulated the effects of climate changing in future on forest composition and forest biomass of typical forest type in northeast of China. We chose three different climate change scenarios developed from GCMs results of ECHAM5-OM and HadCM3:current climate,warmer climate and the state of changing precipitation with higher temperature.The results show as follows,if the climate goes with no change,northeastern forest composition and forest biomass will maintain dynamic balance. Warmer climate is unadvantaged to major forest type in the northeast of China,The percentage of major conifers decrease, along with the percentage increase of some broadleaf trees.The Mixed broad-leaved tree species/Korean pine forest belt in temperate zone will tend to move up.And more warmer,more distinct.Taken account of rainfall further,the forest belt of northeast of China will tend to move northward,rainfall has a little effect on the Mixed broad-leaved tree species/Korean pine forests in temperate zone.