Abstract: With the improvement of electromagnetic yoke insulation performance and voltage resistance level, it is possible to directly connect the yoke with the lines of 220 V or directly connect it to the inverter power supply transformer for the purpose of reducing the weight of the portable magnetic particle testing instrument. By doing so, on the other hand, the potential hazard to safety may arise and in some cases overvoltage may occur, which threatens the safety of equipment and personnel. This paper analyzes the causes of overvoltage, illustrates its harmfulness, and especially points out that the possibility of overvoltage occurs when the excitation current is frequently cut off. Two methods for eliminating overvoltage are proposed. It is advisable to use an alternating current of 220 V to carry out magnetic particle testing if the above-mentioned measures are taken in advance.