In order to reduce pesticide waste of pesticide spraying in the field and alleviate the pollution to the soil, a smarttargeting spraying system on boom sprayer was designed, aiming at satisfying the requirements of spraying for large row spacing and plant spacing. The system was mounted on the common spray boom spraying machine in field, and an ultrasonic ranging sensor, which was corresponding to row and furrow, was set according to a certain distance along spray bar direction. The distance between spray bar and canopy and the distance between spray bar and the bottom of furrow were measured in real time. The vibration noise generated by the uneven furrow and the boom vibration was eliminated by utilizing the signal amplitude modulation. According to the features such as plant height, canopy diameter and canopy height, etc., the amplitude modulated data was carried out in pattern analysis to recognize targets and realize smarttargeting. The equipment test was carried out on the tobacco plant in the field, which has 30cm plant height and 15piece leaves or so. The test results illustrate that, this smarttargeting spraying system has a valuable reference for the design of other target spraying systems. Comparing with continuous spray, the boom sprayer smarttargeting spraying system could save pesticides about 30% and 20% for the gap rate of 39.2% and 31.6%, respectively. Therefore, this smart-targeting spraying system is well performed in the target spraying operation in the fields where the plant space is beyond 15cm and could significantly improve the agricultural economic efficiency.