The invention discloses a tree whitewash device and a using method thereof. The device mainly comprises an arc-shaped roller brush, a distance sensor, an arc-shaped nozzle, a telescopic corner, a signal transmission line, a stretching rod, a thin pipe, a proportional valve, a thick pipe and an electric sprayer. The arc-shaped roller brush is connected with the telescopic corner through a hinge structure and deforms according to a trunk shape under the pressure effect, the telescopic corner slides in the stretching rod, the thin pipe is connected with the arc-shaped nozzle and the proportionalvalve, the thick pipe is connected with the proportional valve and the electric sprayer, and the signal transmission line is connected to the distance sensor and the proportional valve. By means of the device, the defects of the low manual whitewash efficiency, the poor safety and the like and the defects of the poor flexibility and the poor working environment adaptability of an existing whitewash device are overcome to some extent. The tree whitewash device has high working efficiency, the remarkable whitening effect, strong safety, good flexibility and low cost, and can be widely applied totree whitening work.