In RFID systems, when more than one tag responds to the request of reader simultaneously, tag collision would happen. This will cause the reader fail to identify any tag within its interrogation zone. Extensive research on tag collision avoidance have been performed recently. In this paper, we study on the performance of several typical tag collision avoidance algorithms in RFID systems. Lots of simulation experiments have been conducted in order to compare these algorithms’ performance, such as the runninng time and the power consumed. Based on the optimal tree search algorithm, we propose a new tag collision avoidance algorithm OTSA. In algorithm OTSA, we estimate the number of tags within the reader’s interrogation zone first, then we call the optimal tree algorithm to identify the tags. The results of simulation experiments show that algorithm OTSA has better performance when the number of tags within the reader’s interrogation zone getting larger.