Nowadays the need for electrical power is increasing every year. This was caused by the government's policy in providing electrical power to reach all regions in Indonesia. To meet existing needs, the Darajat geothermal power plants must be able to operate continuously. The aim of this paper is to determine the impact on the performance of turbine overhaul before and after the overhaul which can be done by analyzing the obderverd data. The Darajat geothermal power plants operate continuously resulting in decreased plant performance that needs to restore the plant's performance by doing maintenance such as overhoul.. To improve the quality of research results, the authors add literature study, data collection during field observation interviews and discussions with stakeholders and analysis of the performance of the turbine. This results of this study obtained increase in the efficiency of turbine up to 1,78% from the 77,37% before conduting maintainence and 78,75% after maintenance.