Abstract: The domestic AP1000 units have been built and their pre-service inspection is an imminent task, and there is however, a lack of any experience for reference at home and abroad for the inspection. Based on the mechanism analysis on steel safety shell coating dense rust, coating missing and pitting defects, combined with the special structure of steel containment and its special working environment, and at the same time considering the accessibility of a defect inspection method, its coverage area together with its safety and reliability, a set of magnetic adsorption crawling inspection devices equipped with linear array camera was put forward and developed, which was successfully implemented for the pre-service examination of AP1000. This inspection scheme can be widely used in the steel containment and it provides detailed and reliable data for nuclear safety assessment and analysis on the whole shell area and plays a safeguard function for the safe operation of the containment.