To achieve precision application of pesticides and fertilizers to fruiter, a real-time measuring system for fruiter canopy parameters is developed to guide precision spraying in orchard. It can reduce the negative impacts on the environment as well as improve fruit safety. The system consists of crop identification system, vehicle attitude system, master control unit and data logger unit，and a CAN bus is used to connect the microprocessors involved. Primary experiments are conducted on five adjacent trees with regular cylinder-shaped canopy on the campus for three times. Four independent ultrasonic sensors are used to measures the canopy of the target trees on a time-division basis. System sampling rate is 5 times/s; and the tractor-traveling speed of 0.3 m/s is selected. Experiments show that the system can detect fruiter canopy size in real-time, and provide a good measuring and controlling platform for precision spraying based on tree canopy.