Due to the low repeatability and low efficiency of manual inspection, solving the corresponding technical problems to automate the inspection process becomes increasingly important. An automatic magnetic particle inspection system is presented to find defects in complex-shaped mooring chains with nominal diameters of 70-120 mm. Because of the complex shape of mooring chains, a special scanning strategy is proposed to cover the required inspection range during surface crack inspection and welding seam inspection. Thus, on the basis of studying correlative technologies, the scanning strategy, alignment of the detecting arm, finding the start position of inspection and acquisition of indication images are analysed and solved. The experiment shows that cracks in mooring chains can be detected effectively, accurately and conveniently by the inspection system.