A vehicle transmission system is a power transmission device between the engine and wheel load. As the connection hub of the power system, walking system and braking system, it ensures the mobility and safety of special equipment in combat tasks. Firstly, it was demonstrated that transmission efficiency was an important technical index to evaluate the transmission system performance from four aspects: structure characteristics, power transmission characteristics, energy flow characteristics and vehicle dynamic characteristics. Second, the transmission system’s global power loss model framework was developed from the standpoint of generation mechanism and structural features based on the relationship analysis between power loss and transmission efficiency. This gave the transmission system performance characterization a theoretical foundation. Then, the research difficulties and emphases of vehicle transmission system power loss were summarized from three aspects: theoretical numerical study, simulation study and experimental demonstration study. It was noted that the experimental study of large mechanical equipment under complex operating conditions and the simulation analysis of multi-media and multi-parameter couplings can offer guidance for the matching design of the transmission system, performance evaluation, and health management of vehicle transmission components. Finally, it is considered that the comprehensive transmission efficiency analysis under multi-factors and the coupling research of power loss characteristics, efficiency characteristics and performance degradation characteristics based on intelligent algorithms have practical engineering significance for the performance monitoring and evaluation of large machinery equipment.