The invention discloses a tree trunk whitening machine with spraying flow adjustable according to the diameter of a tree trunk. The tree trunk whitening machine comprises a machine frame, a material storage device, a pipeline conveying device, a moving device, a lifting device, a spraying device, a distance measuring device and a controller, wherein the material storage device, the pipeline conveying device, the lifting device and the distance measuring device are arranged on the machine frame; and the moving device is used for driving the whitening machine to move, the material storage deviceis used for containing spraying liquid, the pipeline conveying device is used for conveying the spraying liquid to the spraying device, the spraying device is arranged on the lifting device, the lifting device is used for driving the spraying device to move up and down in the vertical direction, the distance measuring device is used for measuring the diameter of the tree trunk, and the controlleris used for adjusting the flow of the spraying liquid sprayed by the spraying device according to the measured tree trunk diameter. According to the tree trunk whitening machine, the diameter of thetree trunk can be detected and judged, then the number of nozzle openings is controlled according to the diameter of the tree trunk, and the machine has the advantages that the spraying effect is uniform and reliable, the white coating is saved, the spraying is fast, and the terrain adaptability is high.