To address technical bottlenecks such as insufficient seed-filling force, arching of sugarcane seed pieces, and poor filling uniformity in the seeding mechanism of a pre-cut sugarcane planter, a chain-trough belt composite seed arrangement mechanism was designed. The mechanism comprised modular components including a chain-trough conveying assembly, a polyvinyl chloride (PVC) friction belt, and a seed storage bin. The mechanism improved the driving force for seed filling by introducing a friction belt structure, solved the problem of arching and blockage, and enhanced the adaptability of the seed metering device to the morphology of sugarcane seed stems. The working principle of the seeding mechanism was systematically explained, and based on theoretical analysis, the core factors affecting seeding performance were identified as chain groove linear velocity, friction belt inclination angle, and friction belt linear velocity. The EDEM (engineering discrete element method) software, based on the discrete element method, conducted single-factor simulation experiments to reveal the influence patterns of various parameters on the seed filling qualification index and the missing filling index. Furthermore, the interaction between parameters was quantitatively analyzed through orthogonal experiments using the response surface method (box Behnken, BBD). The results show that the linear velocity of the sugarcane trough is the primary influencing factor. The optimal parameter combination is a friction belt inclination angle of 59.84°, a friction belt linear velocity of 0.63 m/s, and a sugarcane trough linear velocity of 0.10 m/s. Under these conditions, the filling qualification index of the simulation model reaches 99.01%, and the missing filling index is only 0.99%. Bench test results indicate that the average filling qualification index of the mechanism is 94.8%, and the missing filling index is 5.2%, verifying that the proposed composite seeding mechanism has good operational performance.