Abstract: In order to improve the unstable system throughput and reduce the "misjudgment" issues, this paper proposes a kind of parallel multi-tree search anti-collision algorithm. Using OVSF code spread spectrum technology, the algorithm can develop tracks in a time slot and when collision occurs, it can identify tags concurrently to reduce the accumulated collision. Theoretic analysis proves that the system throughput is improved with the increasing of code length. Simulation results show that the new algorithm has improved the anti-collision performance of RFID system effectively.