Abstract: Abstract: In order to improve the automatic working performance of orchard sprayer, in this study, an automatically variable-rate orchard sprayer with 40 nozzles and 8 fans based on LIDAR (Light Detection and Ranging) was developed. The high-precision scanning laser sensor was adopted as the detecting source to detecting the canopy parameter. Electromagnetic valve and brushless fan were adopted as actuators to control the flow rate and air volume based on the pulse width modulation（PWM）signals. Each nozzle in the spray system, coupled with a solenoid, achieved variable rate delivery in real time based on the canopy volume. Each side of the prototype equipped four integrated atomization units with one independent brushless fan. The independent brushless fan located behind of atomization unit, and assisted the droplets sprayed from the five nozzles blowing into the canopy, which is conductive to the local regulation of spraying quantity. The brushless motor has the advantages of fast-response, high-speed, and long working-time. The rotating speed of each brushless motor could be adjusted in real-time by PWM signal according to the canopy parameters of fruit tree. The canopy segmentation model was designed to measure the volume and density of canopy, which could meet 3 m height canopy. The canopy was divided into many canopy units, and each nozzle corresponded with one canopy unit and each brushless fan corresponded with five canopy units. A laptop was used to calculate the volume and density of each canopy unit based on the data scanned by laser sensor and the segmentation model. Then the spraying quantity needed forcanopy unit and the air volume needed for five canopy units were acquired by control system. Next, the PWM signals emitted by single chip microcomputer would be transmitted to the drivers of valves and fans to adjust the flow rate and air flow. A total of 48 channel PWM signals were designed for the whole machine, and each channel would be controlled separately. The gasoline generator was adopted as energy source to realize long-working and fully automatic spraying, and the independent brushless fan was used instead of central fan with PTO (Power Take Off)-power to realize partly air volume and use-dosage according to canopy size. The field experiments were conducted in an apple orchard, a research farm belonging to the China Agricultural University, in Beijing. The main tests included the test of deposition distribution in the canopy and air velocity distribution of different height. The tree row space was 5m×2m, the average height of tree was 4.1 m, and the canopy diameter was 2.6m. The environment temperature was 14℃, the humidity was 50.3% and the wind speed was 0.7 - 1.2 m/s. Tartrazine (2.5‰) was chosen as the tracer material and travel speed was 0.8m/s. Water sensitive paper(2.6 cm×7.5 cm) and metallic screen mesh(2.5 cm×7.5 cm) were adopted to receive the deposition for the test of deposition distribution in the canopy. The artificial targets were arranged in the canopy in eight layers with three directions of right, left and middle in each layer. Also, a metal rod was established at the distance of 1.5m from tree center to fix the anemometers. The lowest anemometer was 1.2 m from the ground and the distance of adjacent anemometer was 0.4m. The results showed that the deposits on the front and back of tree were 1.92 and 1.37 μL/cm2, and the minimum number of droplets was 46.2per cm2, which was greater than the requirement of droplet adhesion rate over 25/cm2 in the application of pest and disease control. The coefficient variation of three depths of tree was 14.2%, 18.0% and 13.7%, respectively. The fitting results of canopy contour with deposition and air velocity distribution showed that the designed prototype could realize variable-rate spraying according to the canopy information, which could meet design requirement. In this study, we proposed a new equipment of plant protection for fusiform-type fruit tree, and also provided reference for design and performance optimization for plant protection machinery.