This study introduced a wooden disc measuring method with simple operation and high precision in tree stem analysis. The operational approach can be followed in four steps: (1) Apply digital camera to shoot the dividing ruler placed on the disc; (2) Measure the ring radius by correcting digital images, which is realized by fitting polynomial equation from several fit points; (3) Calculate the coordinate distance between the intersection and the pith through clicking the intersection of lines and the radial of treering successively; (4) Substitute numbers into regression equation to obtain the radius value of ring. Compared to conventional millimeter scale measurement, whose precision reaches only millimeter and sub millimeter, and the professional analysis instrument, whose precision accuracy ranges from 0.0005 cm to 0.0010 cm, this method is more advantageous, with the maximum measure error in radius being 0.007650 cm, the minimum error 0.000040 cm, and the average error 0.002477 cm. With low cost, convenient and simple operation as well as highprecision, this method deserves promotion in analyzing the development of trees.