Abstract: A new type of wall-climbing robot is introduced. Using ultrasonic tandem detecting method, it automatically scans the walls of in-use chemical container to detect potential fault caused by circular weld. This article emphasizes the mechanism, position adjusting and motion controlling algorithm. Moving with magnetic wheels, navigating with magnetic band and detecting with fiber sensor, the robot has the characteristics of compact structure, good navigation performance, feasible position adjusting method and precise localization.