The present invention discloses an anomaly detection method of a current transformer loop. The current transformer loop comprises a current transformer connected with a three-phase power transmissionline, and two first convertors, two first analog-digital converters, a CPU and an alarm which are connected with the current transformer. The two first converters are connected with two three phases of two same types of secondary coils of the current transformer. The two first converters are respectively electrically connected with the two first analog-digital converters, and the CPU is electrically connected with the two first analog-digital converters and the alarm. The anomaly detection method of the current transformer loop does not need shutting and does not need to change the relay protection action strategy mechanism so as to improve the relay protection reliability; and moreover, the anomaly detection method of the current transformer loop is high in detection efficiency and good in accuracy.