Abstract: Local corrosion is inclined to occur to equipment made from AZ31B magnesium alloy after the humid heat test, which is a disadvantage to the service life of the equipment. In this study, with a portable equipment made from AZ31B magnesium alloy as the object, its macro-and micro-morphologies of corrosion are analyzed by Leica ultra-depth of field microscope and SEM, and the causes and mechanisms for the failure are investigated from perspectives of mechanical design and processing, electroless nickel plating, and coating process. It is concluded that the stress concentration and electroless nickel plating with medium volume of phosphorus and defects in coating process result in the corrosion, and that the corrosion is electrochemical corrosion. Based on the process verification and analysis, the improvement measures of corrosion protection for this type of equipment are put forward to promote the environment serviceability and reliability of the equipment.