Most of the flash storage systems reclaim the space occupied by invalid data only when the available free space is low and a data writing request is being processed thereby may intermittently increase the time of carrying out a writing operation and decrease the system performance. For real-time applications, such passive space recycling not only results in tasks suffering long blocking time but also imposes great impact on the predictability of their timing behaviors. This paper presents an active mechanism to recycle invalidated space in flash storage system which, by periodically launching tasks to reclaim data space containing invalid data, can reduce the blocking incurred from space recycling as well as provide a more analyzable recycling operation. The active space recycling mechanism can work well with the wear-leveling mechanism commonly required in flash storage management. In addition, the implementation requires no changes of its host file system. Simulation results show that the proposed space recycling mechanism has significant improvement on the worst case timing behaviors of write operations.