The increase in the number of national electricity customers which is increasing every year must be followed by the availability of sufficient supply of electrical energy from power plants so that there is no energy deficit. Maintenance and overhaul activities are carried out routinely on power plant main equipment so that it continues to be reliable and efficient. Turbine Inspection (TI) overhaul activity at a Gas Turbine Combined Cycle Power Plant is a type of periodic inspection activity carried out at the power unit operated by PT IP. Data on the history of TI overhaul implementation during the 2016 - 2021 period shows that there was a delay in completing the overhaul which resulted in loss of production opportunity. Identification of the causes of waste (waste) is carried out using a lean approach with a combination of the use of Root Cause Failure Analysis (Fishbone and 5W+1H) and Value Stream Mapping (VSM) tools. The primary data in this study is the result of direct field observations and interviews with experts. Secondary data comes from previous TI overhaul implementation history data. The results of data analysis are used to make Current State Mapping (CSM) including the potential for existing waste. Decreasing the duration of TI overhaul is more focused on Critical Path activities which have elements of waste and have a significant influence on the total duration of TI overhaul work. Activity identification falls into the NonValue Added (NVA) category, and Necessary Non-Value Added (NNVA) is used as the basis for making Future State Mapping including corrective steps that must be taken to optimize the overhaul duration to be used in the next OH TI. The total duration of the next TI overhaul, namely GT 4.2 TI 2022 after the implementation of the FSM and all improvement steps that have been made, is close to the standard duration given by the manufacturer, which is 22 days.