In order to solve the problems of high labor intensity,uneven paint and non recovery of lime water for manual painting the tree trunk by lime water,an automatic control rotary lime water sprayer for tree trunk was designed.Through photoelectric detection of the nozzle,the control system controls the arm to drive the manipulator close to the tree trunk,and make each sprinkler reach the appropriate position.The manipulator moves from bottom to top and rotates moderately,at the same time,the spray pump is turned on to extract the proportional lime water and control the spray nozzle to spray evenly on the tree trunk，so as to realize the functions of automatic proportioning, automatic control of spraying lime water and so on,and timely recover the scattered lime water.The application results show that the device greatly improves the working efficiency of lime water spraying and reduces the labor intensity of workers,which has the advantages of convenient operation, flexible movement, better stability.