Once China’s Tianwen-1 Mars probe arrived in a Mars orbit after a seven-month flight in the deep cold space environment, it would be urgently necessary to monitor its state and the surrounding environment. To address this issue, we developed a flexible deployable subsystem based on shape memory polymer composites (SMPC-FDS) with a large folding ratio, which incorporates a camera and two temperature telemetry points for monitoring the local state of the Mars orbiter and the deep space environment. Here, we report on the development, testing, and successful application of the SMPC-FDS. Before reaching its Mars remote-sensing orbit, the SMPC-FDS is designed to be in a folded state with high stiffness; after reaching orbit, it is in a deployed state with a large envelope. The transition from the folded state to the deployed state is achieved by electrically heating the shape memory polymer composites (SMPCs); during this process, the camera on the SMPC-FDS can capture the local state of the orbiter from multiple angles. Moreover, temperature telemetry points on the SMPC-FDS provide feedback on the environment temperature and the temperature change of the SMPCs during the energization process. By simulating a Mars on-orbit space environment, the engineering reliability of the SMPC-FDS was comprehensively verified in terms of the material properties, structural dynamic performance, and thermal vacuum deployment feasibility. Since the launch of Tianwen-1 on 23 July 2020, scientific data on the temperature environment around Tianwen-1 has been successfully acquired from the telemetry points on the SMPC-FDS, and the local state of the orbiter has been photographed in orbit, showing the national flag of China fixed on the orbiter.