Abstract: Two detailed investigation were made of public welfare forest resouces in 1999 and 2008. In different forest types,on the basis of the area and volume dynamic change characteristics,the volume of biomass conversion factor method was used for calculating the public welfare forest biomass and carbon stock. The results showed that from 1999 to 2008, the per unit area biomass of public welfare forest increased from 72.33 t·hm^-2 to 113.33 t·hm^-2, the average annual growth rate was 4.91%; Total biomass increased from 253.33×10⁴ t to 396.9×10⁴ t, which had 143.60×10⁴ t growth. Total carbon increased from 122.66×10⁴ t to 198.47×10⁴ t, having 75.81×10⁴ t growth and 5.25% average annual growth. Through many years of establishing public welfare forest,its stand structure became gradually optimized,its biomass and carbon accumulation increased effectively, therefore its ecological function had a great improvement.