WtE of MSW plays a crucial role in renewable energy production in Korea. Municipal solid waste (MSW) is an important energy resource for combined heat and power (CHP) production. This study investigated an increasing method to the power generation efficiency by MSW to energy (WtE) plants in South Korea and discussed the issues related to energy efficiency improvement. In some cases, however, achieving a high energy efficiency of WtE is not practical due to various technical and non-technical reasons. The design and operation of a WtE plant is determined primarily by the amount of MSW to be treated, not by energy demand. The majority of these new facilities feature a very high efficiency with respect to both energy recovery and environmental performance. But they not only recover energy from waste, they also have the potential to facilitate a high material recovery. With their high energy efficiency they contribute even more to the reduction of greenhouse gases than earlier generations of WtE facilities. It is important to have this in mind in the strategic planning of both waste handling and energy production. Improving power generation efficiency is required for new power plants producing steam at pressures higher than the current level of 20-30 bar. The power generation efficiencies of the economizer outlet temperature of 190 ℃, NCV value based on 2,300 kcal/kg and exhaust gas discharge 5,000, 6,000, 7,000 m3/ton changes are improved are 1.14, 1.36 and 1.59 %. And exhaust gas discharge 5000 m3/ton was showed that increasing the power generation efficiency was higher 28.3 % comparing to gas discharge 7000 m3/ton. Excess air ratio changing in accordance with the calculated power generation efficiency results, as the excess air ratio decreases boiler and the power generation efficiency is increased. The power generation efficiency according to the change in the amount of gas boiler times 7,000 m3/ton, NCV 2,300 kcal/kg and excess air ratio based on the excess air ratio of 1.8 is increased with the excess air ratio decreases . Increasing the power generation efficiency was about 0.2 - 1.64 %. Also it has been shown to decrease the resulting power generation efficiency was 0.41 % increase in the excess air ratio to 2.0.