Software-defined networking (SDN) has been gradually applied to tactical mobile ad-hoc network (MANET) routing research recently to provide better quality of service (QoS) than that of traditional MANET routing protocols for the increasingly abundant tactical maneuvering tasks. However, due to the strong variability and distributed structure of MANET, there are many problems in the application of SDN technology to MANET routing that need to be solved urgently. Starting from the status quo of tactical MANET routing, this paper explains the traditional MANET routing protocols and SDN technology and summarizes the existing MANET routing methods combined with SDN. Then, problems that need to be solved in the application of SDN to tactical MANET routing are discussed around the routing process, including the control layer reliability, flow table issuing time, control overhead, mixed network elements, and scalability. Corresponding methods are expounded from the perspective of the SDN structure. Finally, the issue of future research directions is discussed.