The peak load of electricity in Korea usually take placed in summer, but now a day it replaced by winter. This is because electricity appliances are used to heating instead of oil or gas boiler in commercial and residential sector. Since electricity can’t be stored, instant production response to demand is necessary. As peak load is prospected to be higher than before, the capacity of power plant have to be expanded to meet instant high electricity demand. If the peak load can be distributed to non-peak load, the required power plant capacity is reduced. In other words, we can save power plant construction cost. In addition, the load factor is increased under peak load distribution. So, lower priced fuel fired more expensive power plant is more attractive than higher priced fuel fired cheaper power plant. To take these advantages, some countries try to introduce smart grid. It encompasses wide range or works including electricity demand redistribution through communication with customer using digital technologies. But we only consider the cost saving effect through peak load redistribution under smart grid scheme. In this study, power plant expansions under various scenarios are planned. WASP-IV is used to calculate the effect of power plant construction reduction.