Abstract: With the continuous expansion of distribution networks, insulation faults caused by partial discharge in internal cables of 10kV switchgear are increasingly common, posing a serious threat to the reliability of the power supply system. As an important means of early warning for partial discharge, ultrasonic testing still faces significant challenges in accurately identifying signals and diagnosing faults under complex on-site interference conditions. This paper, based on an actual case of abnormal ultrasonic detection in 10kV switchgear at a substation, systematically analyzes the discharge characteristics of cable terminals and their signal features in the ultrasonic frequency range, achieving precise fault location, improving diagnostic accuracy, and proposing effective treatment and improvement measures, providing practical guidance for enhancing the maintenance level of distribution network equipment.