A method and system for real-time measurement of the height of a spray boom (1) relative to a crop canopy, wherein the method comprises the following steps: step 1: calibrating ultrasonic distance measurement sensors (14, 16, 19, 20); step 2: determining the angle between two ultrasonic distance measurement sensors (14, 16); step 3: acquiring the relative height of a spray boom (1) and a crop canopy; step 4: performing anti-interference processing of height acquisition data; and step 5: calculating the relative height of the spray boom (1) and the crop canopy. The system is characterized in that two ultrasonic distance measurement sensors that form a certain angle are mounted on two tail ends of the spray boom (1) respectively, to effectively acquire the height of a crop canopy under the action of a control unit (3), and obtain the relative height of the spray boom (1) and the crop canopy after anti-interference analysis and conversion of data, thereby implementing accurate monitoring of the relative height of the spray boom (1) and the crop canopy when the spray boom (1) is inclined, and breaking through the technical bottleneck of being unable to accurately obtain the relative height of the spray boom (1) and the crop canopy when the spray boom (1) is inclined due to jolt during field operation of a boom (1) sprayer, thus laying the technical foundation for the dynamic adjustment of the balance and height of the spray boom (1).