The Lahendong Unit 3 geothermal power plant (PLTP) is a PLTP type of dry steam power plant and the thermodynamic cycle that occurs in the system is the Rankine Cycle. The objectives of this study are: a) Analyzing the temperature of the influence of the main air cooler on the performance of the turbine unit in Lahendong Units 3, b) Analyzing environmental factors that affect changes in the temperature of the cooling air which serves to improve its ability to repair the turbine. The method used is a survey method. The data used in this study is PLTP operation data for one month which is used to find turbine solutions to compare with the temperature of the main cooling air and ambient temperature. Resulting from the temperature of the main cooling air (cooling tower outlet) increases, the performance of the turbine shows a low number, on the contrary the temperature of the main cooling air increases, the performance of the turbine will rise. Factors that influence the main air temperature, the temperature and the temperature of the cooling tower inlet or the temperature of the air coming out of the condenser