Abstract:The systematic underestimation error of forest timber by using standard sample trees was pointed out. And 2 correction methods were proposed with easy estimation of the correction factors from the sampling data. The traditional formula is In contrast. the corrected formula is where V(TE) and are V1(TE) the estimated timber volume for whole quadrat using the original formula and the corrected formula respectively. VBK and ABK are respectively the measured timber volume and breast height cross-sectional area of K‘th standard sample tree. AT is the total breast height cross-sectional area in the quadrat; hB and dB are respectively the height and breast diameter of the tree with average breast height cross-sectional areal dw is the average breast height diameter weighted by breast height cross-sectional area ; an db is the slope of the tree height curve at d=dB, dB, hB and dw can be es timated by sampling in the quadrat. b can be obtained either from given tree height curve or by applying linear regression to the same sample data for estimation of dB, hB and dw. The second correction of tEe formula has exactly the same form as the above equation, except the n standard sample trees are selected to have breast height diameters closest to the average breast height diameter in the quadrat. Thus dB and hB should be replaced by statistically estimated average breast height diameter and average tree height in the quadrat.