In order to solve the problem of accurate measurement and control of the distance of the spray rod relative to the crop canopy when spraying solanaceous crops such as potatoes, a set of spray rod height control system of the potato sprayer was designed. The system adopted 2d laser radar scanning field potato plant canopy, according to the potato planting pattern of crop canopy crown unit segmentation, through the fusion of attitude sensor data on radar output data correction, and based on the median filtering algorithm, moving the least squares curve fitting method processing crown point cloud data, real-time calculate the vertical distance of crown relative information, and the fusion cylinder displacement sensor designed double threshold spray rod height control strategy, realize the precise control of spray rod relative potato crown height. The system was applied to the 3WP-1500 sprayer，and the system performance was tested by height detection precision test and height adjustment test. The test results showed the maximum relative error of the crop canopy height detected by LiDAR was 7.16%, and the average relative error was 3.95%. The height adjustment test showed that by determining the optimal adjustment threshold, the spray bar height adjustment error can be effectively reduced, and the system stability can be improved, and the standard deviation of the test height adjustment was 21.81mm, and the average relative error was 3.08%, and the system ran smoothly to meet the automatic control needs of the relative canopy distance of the spray bar.