In order to ensure the application effect of plant protection, the proper distance between spray boom and plant canopy need to be maintained when field surface relief and soil hardness were changed during the whole working period. Three ultrasonic distance measuring sensors were used to obtain the height information of spray boom, and the sensors data were preprocessed with amplitudelimiting and moving average algorithm. Two dualaxis inclination sensors were used to obtain the posture information of sprayer and spray boom which were installed on the chassis of sprayer and spray boom respectively. And then multisensor fusion algorithm based on weighted average was used to handle the spray boom height information. Then different control strategies were designed for different working states of sprayer by using expert knowledge and experience. According to the established control strategy, the control signal was outputted by the inference engine of expert control to control mechanism which was used to drive the spray boom height adjustment cylinder. The mechanical structure of the boom system was introduced, and the composition and working principle of the boom height intelligent adjustment system (BHIAS) were described. The control algorithm and software realization of BHIAS were elaborated. The work status of external variable spraying system was obtained by CAN bus to achieve synchronization of work status between BHIAS and variable spraying system. The touch screen was used to achieve humancomputer interaction and control parameters was sent to the controller for boom height control, such as amplification coefficient, attenuation coefficient, adjustment tolerance, etc. The BHIAS was applied to 3WZG-3000A boom sprayer which was developed by the research group. Ground tests were conducted separately for testing the adjustment performance of BHIAS. The test results showed that BHIAS can follow the boom height adjustment requirements which was caused by step excitation quickly. When the allowable error of boom height adjustment was 8% and the height of step excitation was 20cm, the maximum adjustment time of BHIAS was no more than 0.75s. 