Abstract: With the increase of train speed, and the CTCS Center couldn’t judge and treat it in time, it might cause the mistake of low frequency code sequence and signal display upgrade, thereby damaged the traffic safety. This paper took the interlock method of “The Three Section Inspection” into the analysis and judgment of section shunt state, led the concept of running interval in automatic blocking, judged the track circuit section failure as much as possible, combined with the relevant measures for the protection to avoid accident and ensure traffic safety.