In this paper, we drew new security threats on IoT (Internet of Thing) based smart battlefield environment and proposed countermeasures against them. DoD (Department of Defense) is focusing its attention on the development of unmanned combat systems (UCS) to prepare for future war. The IoT technology provides networking service to connect each other unmanned combat system. But, IoT has the security vulnerabilities of each element of the technology itself because the technology integrates several components to configure a specific service. And new security vulnerabilities will be caused when they are interconnecting. If we fail to defend the security threat that may arise from IoT based smart battlefield environment, we can’t obtain intelligence superiority and furthermore will not be able to assure the victory of the cyber war. In smart battlefield environment applied to IoT, we can draw four main security threats; illegal remote control, information leakage, false information insert, and signal disturbance. And we propose countermeasures in response to these security threats; authentication, access control, intrusion prevention, and cryptography technology.