Metal Oxide Surge Arrester is one of the most important equipments in electric power system.Because MOA bears the system voltage all the time and ages

the resistance leakage current will increase and generate heat.The performance of MOA may become inferior.Whether its running status is good or not directly affects other equipments in system.So it is necessary to detect performance of MOA periodically.For this purpose

the scholars at home and abroad have brought forward various methods to judge MOA function superior or inferior.In the basis of analyzing MOA operating principle and be based on practical experience

the paper suggests a new method with using phase difference for judgment.The experiment shows that the method is more clear

accurate and convenient to carry out a judgment for function of MOA.