Abstract: To address the issues of high labor intensity and low efficiency associated with manual magnetic particle testing of welds in large cylindrical tanks, an automated magnetic particle testing robot was designed in this study. First, a mechanical model for the robot’s wall-moving motion was established based on the tank inspection environment. By analyzing its wall adhesion and motion forces under a no-slip condition, the required minimum adhesion force was determined. Based on this, the structural design and simulation of a permanent magnetic adhesion wheel were completed, the influence of permanent magnet and magnetic yoke thickness on adhesion performance was investigated, and the required torque for the drive motor was subsequently calculated. Second, a robot control system based on a master-slave architecture was developed, with data interaction achieved via a wireless local area network. The robot body used an STM32 single-chip microcomputer as the microcontroller, while the host computer, with an industrial computer as the core processor, was responsible for weld seam identification and tracking tasks. Additionally, a magnetic particle detection system integrating a magnetometer and an automatic stirring and spraying device was designed and assembled. Finally, a robot prototype was constructed, and magnetic particle testing validation was conducted. Finally, a robot prototype was built and magnetic particle testing verification was carried out. The results show that the robot can stably move along the weld on the tank wall. When tested with the A1−15/100 standard test block, both the circular and cross-shaped magnetic indications are clearly displayed, and the sensitivity meets the national standard, achieving automation of magnetic particle testing for welds. This study provides a complete technical solution and equipment reference for the automated magnetic particle testing of welds on large cylindrical tanks, and has practical application value for promoting the automated nondestructive testing of similar structural components.