| The purpose of this study was to design an automatic spraying device for tea garden in hilly and mountainous areas to solve the problems of low automation, serious waste of liquid medicine and inaccessibility of large and medium\|sized devices. Based on the actual conditions of tea gardens, the structural design and theoretical analysis of the main parts of the automatic spraying device were carried out. The device adopted a spraying mode of horizontal line and 45° angle direction, combing with the ultrasonic ranging module to automatically target to achieve positioning between the nozzle and the surface layer of the tea crown. The length of the spray bar was calculated to be 1.1 m, and three nozzles were on one side of the spray bar, with a nozzle spacing of 0.5 m. The spraying control system took STC89C52 as the microcontroller and used C language programming to realize the automatic adjustment of the spraying distance of the spray rod, as well as the control of the motor and solenoid valve. Taking canopy gradient, spray height and walking speed as experimental factors, the droplet deposition density was used as the performance index to conduct orthogonal experiments. The results showed that the canopy gradient had a extremely significant effect on droplet deposition density（P<0.001）, but spray height and walking speed had no significant effect on it（P>0.05）. The effect on droplet deposition density was from big to small in order of canopy gradients. The average droplet deposition density at each point of different canopy gradients was greater than 26·cm-2, meeting the requirements of spray size definition of 20·cm-2. |