To reflect interactions between users and “damage & protection simulation system about battlefield target”, functional requirement was captured with use-case modeling technique. On elaborating basic method in description about damage & protection simulation need for battlefield target, identify participants in the simulation system, identify use case of simulation system in accordance with participants, control the system behavior with use case diagram, describe specific use case on document form of use case stipulation in establishing use case model about damage & protection simulation system. Finally, further refinement was achieved by activity diagram with "Call Damage Assessment Model", which demonstrated the whole process of requirement modeling for simulation system driven by use case.