Study of a Rotating Detonation Engine (RDE) has been carried out in many research institutions. The RDE has the advantage of high efficiency, simple structure and short combustor length. Toward the practical use for rocket engines, the evaluation of thrust efficiency at vacuum condition is necessary. In addition, it’s necessary to find a cooling method to endure the high heat load by detonation combustion. In this study, ethylene - oxygen mixtures are used as propellant, and we applied C/C composite, which is a heat resistant material, to a RDE and carried out a long-duration combustion test at sea level. As a result, we succeeded in the long-duration rotating detonation engine combustion demonstration of 6- 10 s at sea level for the first time in the world as rocket engine use, and the maximum thrust and the maximum specific impulse were achieved 301 N and 144 s.