In this paper, to overcome the deficiencies of the existing technology for the off-orbit problem of satellites, a space sail unfolding device is proposed, which realizes the functions of large-scale flexible sail stowage during the launching stage and sail unfolding in the orbit, and the device has the features of modularized combined use, repeatable folding and passive drive. This paper designs the layout and structure of the de-orbiting sail, clarifies the working form of the de-orbiting sail, analyzes the influence of the de-orbiting sail's unfolding synchronization, conducts modal analysis of the de-orbiting sail's storage and unfolding states, monitors the operation and action of the mechanism through the feedback data of the sensors and carries out the simulation and experimental analysis of the de-orbiting sail, so as to complete the de-orbiting task for the reliability of the target.