Insulation and protection system as parts of high voltage system, they can improve stability and reliability of distribution system by correctly designing and using of proper equipment. Surge arresters have been used to protect distribution system of Provincial Electricity Authority (PEA) form lightning and switching surge. In this paper, a modeling of Metal Oxide Surge Arrester (MSA) in 22 kV distribution systems was designed using ATP-EMTP program. The simulation results were compared with experimental results of surge arrester sample model. The comparison results are indicated that the error percentage of leakage current less than 4.4 percentages. The proposed model can be used to analyze impact of leakage currents of in the distribution system. Moreover, it can be used to predict lifetime of Zinc Oxide surge arresters.