Abstract: Young tree target is hard to detect in orchard spraying. In order to solve the problem, a young tree target detector was designed based on infrared sensors. Spraying parameters, such as spraying width and delay distance, could be input to the detector easily. The detector could probe orchard tree trunk on the both side of the sprayer at the same time, and accurately control solenoid valves after calculating spraying position on the basis of spraying parameters. Laboratory experiments indicated that accuracy of the detector was hardly affected by probing distance and diameter of tree-truck, while it was affected by the speed of sprayer a little. When the trunk is in the detection range of infrared sensor, and the speed is not more than 1 m/s, the calculating accuracy of spraying width is not less than 96.1%. Orchard experiments shows that the probing accuracy of the detector is 100%, when the speed of sprayer is not more than 0.94 m/s.