Abstract: Utilizing variable BEF(biomass expansion factor) method,a switch model between stand volume and forest biomass was established.In this paper,the difference between wood air-dry density and over-dry one was presented firstly and its influence on carbon density calculation was analyzed,moreover the correct coefficient was obtained.Utility model was used to calculate the stand carbon storage by forest biomass,which making the sub-compartment stand volume's transformation to carbon storage come true based on the forest resource programming and investigating and it was educed by the differences of chemistry element proportion and the molecular weight of wood.Utilizing the model,the authors obtained the average carbon density of stand in the study region,which was 85.06 and 88.13 t/hm² in 1994 and 2002 respectively.Including the losing carbon storage of 158 785 t between years of 1994 and 2002,resulted from forest accretion cutting,the total increase of carbon density was 1.10 t/(hm²·a).Using GIS software,the distribution of carbon density in 1994 and 2002 was explored and superposed.The results show that the area of carbon density increased is a little more than that of carbon density reduced.The important reasons for carbon density reduction are forest tending and illegal cutting.