The imbalance in the growth of generating capacity with electricity growth requires the existing plants to continuously increase the efficiency and reliability. Climate change makes the ambient temperature rise every year. The Gas Turbine efficiency is greatly influenced by the work of the compressor. Here, a case will be taken at the Block 2 UP PLTGU Muara Karang, Jakarta. During the day, Gas Turbine is only capable of producing 230 MW of power and cannot reach the maximum capable power as in the condition when the commissioning is 250 MW. The decreasing performance of Gas Turbine is partly due to the high inlet temperature of the compressor. In this paper, fogging system is applied in inlet air filter to reduce inlet air temperature in order to increase compressor efficiency. The result shows that with certain fogging system design and with droplets diameter of 20 μm, it can reduce the ambient air temperature by 0.6739 °C every second.