Abstract: This article focused on the abnormal data of ultrasonic partial discharge of 10 kV GG switch cabinet. By analyzing and comparing the abnormal data of ultrasonic partial discharge in front and back cabinets, the obvious discharge characteristic quantity and the abnormal signal location was found. And then combined with power outage applied voltage test to verified the conclusion. Thus, the discharge location and discharge type was founded. Because of the deterioration of the insulation of the current transformer in the cabinet, the ultrasonic partial discharge is out of the standard. The hidden danger of equipment can be eliminated in time after replacing the three current transformer.