Abstract: The diameters of trunks and branches of the standing tree are important working parameters of intelligent pruning robots.This paper presents a method based on computer vision to measure the diameters of trunks and branches of the standing trees.A gauge,whose size was known,was used to simplify the calibration of CCD camera without nonlinear aberrations.Firstly,the images of gauge and standing tree were acquired by CCD camera.Secondly,the template was detected by twice template matching,the number of pixels in the area of gauge in the image was counted.Thirdly,the actual size of a pixel in image was got by dividing the size of gauge by the number of pixels in the area of gauge.Fourthly,trunks and branches of standing tree were detected by the joints of them,and then the numbers of pixels of trunks and branches were counted.Finally,the actual diameters of trunks and the branches of standing tree were got by multiplying the numbers of pixel of trunks and branches by the actual size of a pixel.The diameters of 12 trunks and branches were got in the experiments,and the mean absolute error was 0.67 cm,while the mean relative error was 1.9%.The results of experiments show that the method presented in the paper can exactly get diameters of trunks and branches of standing trees.When the diameters of trunks and branches of standing trees in a complex background are measured by this method,the precision will be improved.