Abstract: UAV spreading has been widely used in modern agriculture in recent years. However, the scattering behavior of granular materials can often be produced during spreading. At the same time, the material residue in the trough cannot be fully cleaned up, when the trough wheel is used to discharge materials. In this study, a strip seeding device of the unmanned aerial vehicle was proposed for the granular fertilizer application. Firstly, a variable-diameter groove wheel was designed, according to the principle of cam motion. The traditional groove wheel was split into several parts, such as the groove and the central shaft. The central shaft was replaced with a camshaft as a fixed part. The rotation of the camshaft was used to realize the discharging fertilizers for the cyclic changes. The discharge volume rose in steps with the increase in rotational speed. Finally, the gap then decreased to stabilize and slightly decline in the trend of change. A deflector device was also designed with adjustable work spacing. A layered pattern was used to centralize the overall device. The spacing between rows was adjusted via the outlet direction of the guide tube and the angle between adjacent tubes. The row alignment was realized to avoid the redundant structure in the actual operation. The whole device was driven by electric power. According to man-machine communication, the microprocessor was used to realize the regulation on the rotational speed of the groove wheel, the size of the wind power of the culvert system, and the working distance of the rows. The simulation model was also established for the fertilizer discharging of the strip applicator. A bench test was adopted to verify the simulation using the discrete element software (EDEM). A systematic investigation was then implemented to explore the effects of the structural parameters of the variable-diameter grooved wheel and the rotational speed on the movement of the fertilizer particles during operation. The optimal structural parameters of the fertilizer discharger were obtained after optimization. A comparative test was carried out to verify the variable diameter grooved wheel. The bench results show that the better uniform discharge was achieved among different pipes of the device, with the highest coefficient of variation of 1.30%, and the highest discharge of 453 g/s at 120 r/min; The better performance of the reducer chute wheel was achieved at the same rotational speed, compared with the ordinary ones. The simulation results show that the variable-diameter chute wheel was better and faster at discharging the material in the trough. A comparison was also made on the amount of fertilizer particles backfilled under the same rotational speed of the two types of tank wheels. The reducer tank wheel significantly improved the issue of material residue. The field test showed that the angle of the guide tube also dominated the row spacing and striping index. The better striping was achieved in the minimum striping index of 39.6%, indicating the rationality and feasibility of this device. The finding can also provide a strong reference to design the striping device in unmanned aircraft.