Abstract: The setting of overlap is the key technology of train over speed protection for automatic train protection system. The overlap is conventionally set up controlled by the interlock subsystem after the end of movement authority (EOA), related to a number of factors, and its calculation model is different. According to the specific parameters of the actual turnback station, the article calculated the driving influence of overlap under the mode of communication based train control (CBTC), analyzed the relationship between the overlap and turnback efficiency. The results of simulation and calculation showed that if the overlap was too small, it would lead to slow driving and less stopping, also lead to the turnback tracking interval too long, and reduce the efficiency of turnback. Therefore, it was needed to consider the reasonable overlap.