In practical power supply system, voltage always exists between neutral wire and earth wire. Excessive neutral-earth voltage in machine room will not only influence the communication and cause the increase of error rate of data transmission, but also damage network equipment. Some equipment (such as server and minimal machine) is supplied with neutral-earth voltage detection circuit. Once neutral-earth voltage exceeds a certain specified value, the equipment cannot start up. This paper mainly analyzes reasons of excessive neutral-earth voltage in machine room and puts forward corresponding solutions and specific measures.