Abstract: Due to communication delay and ranging error, the ZC (zone controller) needs to accurately calculate the train safe position according to the train reported position while taking comprehensive consideration of factors such as current running speed and communication delay. The premises for calculating the train safe distance by ZC is introduced， and the principle of calculating the train safe position is expounded. The principle and rule of train safe position calculation in current ZC jurisdiction area and in adjacent ZC common jurisdiction area are discussed respectively, the handling of different abnormal situations are summarized.