［Objective］With the high-speed development of urban rail transit, the drastic increase of passenger volume puts forward higher requirements on the train departure interval. In order to optimize the information transmission process, shorten the train departure interval and meet the higher operational needs, it is necessary to analyze the limitations of the adopted vehicle-wayside communication mode in CBTC (communication-based train control) system when calculating movement authorization, and study a new optimized movement authority method.［Method］The definition of movement authorization and its calculation principles are introduced, and the differences between CBTC system and TACS (train autonomous control system) are analyzed. A train interval control method based on cellular automata is proposed, and a movement authorization calculation model considering relative speed is constructed, to optimize movement authorization from the model level. Taking the alternate post-station turn-back at Shenzhen Metro Line 3 Liyuan Station as an example, the movement authorization optimization model proposed from using MATLAB software is verified under both CBTC and TACS systems.［Result & Conclusion］When the turnout speed limit is 35 km/h, the post-station single-track turn-back time interval under TACS is 34 s shorter than that under CBTC system, significantly improving train departure efficiency.