Anti-Collision is one of the key problems in RFID system. Aiming at the deficiency of Query Tree Algorithm that the complexities of query and communication are increased due to adding prefix seriatim, an improved algorithm called Collision Tracking Tree Algorithm is proposed, which updates query prefix using collision position. By designing the collision position tree, the communication complexity of this improved algorithm is analyzed theoretically. On the assumption that the collision bits are continuous, three lemmas and a theorem about the reader communication complexity are presented and proved in detail. Finally, the performance of the algorithm is simulated by using MATLAB. The simulation results show that the reader communication complexity of collision tracking tree algorithm is better than the query tree algorithm based on the assumption that the collision bits are continuous. So, in the normal instance using the proposed algorithm can reduce the complexity of communication and save costs of the system effectively.