Abstract: The bolt holes of the reactor pressure vessel are an important component of the pressure vessel head equipment. Due to the fact that each major refueling overhaul requires the opening and closing of the top cover of the reactor pressure vessel through the screwing out and screwing in of the main bolts, the main bolt holes of the pressure vessel are prone to contact damage. A video scanning device for the inner surface of threaded holes was developed to address this issue. The development plan and system composition of the device were introduced, inspection of holes of pressure uessels and functional testing was conducted on the device. The test results showed that the device can walk around the central axis on the flange surface of pressure vessels had accurate movement, good reliability, clear and visible captured video images, low distortion rate, and met the usage requirements. At the same time, the video scanning device had a high degree of integration, simple operation, and both manual and automatic modes, which can significantly reduce the radiation dose borne by on-site workers and improve the efficiency of in-service inspections.