A novel method to detect ferroresonance was proposed based on the drastic characteristics of the electromagnetic voltage transformer (PT) current rate. This scheme takes current rate which is greater than a threshold value as starting signal and judges the occurrence of resonance by detecting duty ratio of the peaks and interval angles. Then, it identifies the periods and patterns established on the interval time of spikes. Through simulation testing of MATLAB, it can distinguish the occurrence and types of ferroresonance accurately, which verifies the validity of the detection method.