Abstract: Abstract: In order to solve the problems when ultrasonic atomization transducer was used for ultra-low-volume spraying pesticides, i.e. the atomization flow was little and the transducer's structure was complex, this paper presented a new structure of agricultural ultrasonic atomization transducer based on the atomization requirements proposed by the working principle of ultrasonic atomization transducer and agricultural pesticide spraying. The transducer mainly consisted of a venturi tube, a cylindrical square-cavity, an ultrasonic vibrator, a rubber washer and a flange cover. When the high-frequency alternating current (AC) voltage was applied on the ultrasonic vibrator, liquid was atomized. In the meantime, the circumscribed air pump formed the air vortex in the square-cavity, which would drive the droplet to rotate and move upward, prevent the spread of droplet and avoid attaching on the inner wall of the vessel. Firstly, the parametric model of the ultrasonic vibrator was established and then optimized with ANSYS parametric design language (APDL) to control the droplet diameter of the transducer within the setting range and maximize the atomization flow. In the atomization process, we chose the electrode diameter and the thickness of the ultrasonic vibrator as the design variables, the vibration amplitude of the ultrasonic vibrator as the objective function, and the driving frequency as the constraint condition. Secondly, penalty function was used to solve the optimization problem with inequality constraints. Meanwhile, the modal assurance criteria (MAC) were adopted to recognize the target modals intelligently by ANSYS finite element software. If the value of MAC was closed to 1, the target model was similar to the reference model. This indicated that the vibration along the axial direction was concentrated on the surface of the ultrasonic vibrator and the vibration amplitude was larger than other models. Thirdly, a prototype built based on the optimization results was manufactured to conduct the atomization flow measurement experiment and the droplet diameter measurement experiment. The measured resonant frequency of the optimized transducer was 1.53 MHz, which was very close to the simulated value of ANSYS finite element software (1.62 MHz) and the error was 5.9%. The measured resonant frequencies of the transducer before and after optimization were 1.56 and 1.53 MHz respectively. When the excitation frequency was at the resonant frequency 1.53 MHz, the atomization flow rate of the optimized agricultural ultrasonic atomization transducer reached the maximum. If the excitation frequency of the ultrasonic atomization transducer was lower or higher than the resonant frequency, the atomization flow rate would be reduced, which illustrated that the ultrasonic vibrator should work in the resonant frequency to make the transducer produce the largest amount of aerial fog. The maximal atomization flow rate of the agricultural ultrasonic atomization transducer increased from 1.20 to 1.29 g/min when applying an AC sine-wave voltage whose peak-peak value was 100 V, that was, it was raised by 7.5% compared with the flow before optimization. At the same time, the VMD (volume median diameter) of droplet measured by a laser particle size analyzer (Winner318B) was consistent with the design requirement. Research results provide a scientific reference for optimum structural design of agricultural ultrasonic atomization transducer and the increase of the atomization flow.