In the power system, wall bushings play a critical role by connecting power equipment with external power networks, ensuring a secure and dependable power supply for equipment operation. However, structural defects often lead to deterioration and breakdown of wall bushings during operation processes. This study analyzes the insulation defects of wall bushings at different operation durations. Firstly, an equivalent model of the wall bushing is constructed by applying COMSOL software, the location of the electric field distortion was identified. Subsequent partial discharge and ultrasonic detection results at the position of wall flange could clearly distinguish the differences in insulation performance of wall bushings at different conditions. The partial discharge detection results showed that the wall bushing with in-bulk insulation damage exhibited significant abnormalities in terms of increased discharge capacity. According to the ultrasonic testing results, the wall bushing with regular insulation performance exhibited no discernible defects, while the wall bushing with in-bulk insulation damage displayed three distinct defect waveforms. Such combined detection methods provide a practical path to evaluate the insulation performance of wall bushings at different operation durations, and thereby enhances the safety and reliability of power systems in engineering applications.