Based on the importance of battle damage assessment (BDA), a basic procedure and research method of equipment damage level assessment is proposed, which is based on the functional task decomposition of equipment, the description of functional structure and the determination of battlefield repair replaceable unit. The estimation methods of repair influence coefficient and function influence coefficient of components are put forward, and the comprehensive evaluation algorithm of equipment damage level based on battlefield repair time and task function influence is innovatively established. The results show that the method can provide reference for equipment damage level assessment and battlefield repair.