In view of the existing problems of preventive maintenance measures for a certain type of UAV line-of-sight link system, a multistate multi-valued decision diagram (MMDD) model is proposed based on the main dynamic gates in the dynamic fault tree of the multistate system, such as the priority and gate PAND and the functional correlation gate FDEP. The failure products of the link system are analyzed, and a new preventive maintenance strategy is formulated through the reliability analysis method. The results show that the model can improve the reliability of the equipment and realize the maintenance optimization of the UAV link system.