In order to match the requirements of MQ—600 type air-assisted boom sprayer, the axial fan for air-assisted duct was designed. According to final velocity principle of air-assisted duct on crop canopy, the fan’s air flow, air pressure and the flow velocity and other parameters were determined. The key parameters, such as ratio of axial fan speed, wheel hub ratio, diameter, blade pressure distribution of the whole flow cross-section were calculated. Then, the selection of fan blades, blade chord length of each section was calculated. According to the designed parameters, the physical prototype was built and its performance was studied. The results showed that when the fan speed was under 1473r/min, the outlet wind velocity of the duct was 32.1m/s, and the wind velocity was 8.6m/s at the 0.5m blow the duct, which means the fans met performance requirements. 