Abstract: The length of the approaching section of the train affects whether the train enters the red light or not, and then affects the efficiency of the train operation. For different station types, this article studied the influence range of shunting route, departure route and approach section of receiving route. According to each group of cases, the paper designed the methods and measures of extending the approaching section. Referring to the relay interlocking circuit, the interlocking logic of the signal machine approaching the lock in different cases was implemented, and the safety of train operation was improved.