Abstract: The fire protection system is one of the important systems of KM6 horizontal cabin. It is different from ordinary ones due to the specific environment inside the cabin. The essential considerations for designing the system are analyzed in this paper, and a detailed set of fire protection plan is presented incorporating currently leading technologies in the world. It has been proved by test that the system is conceptually advanced and that it meets the requirements of combined astronaut-spacecraft-space suit test in the KM6 horizontal cabin.