The electrical energy needs grow every year, increasing awareness and use of renewable energy even higher. Geothermal power plants (GPP) are even ogled as a renewable energy source that has a lot of potential worldwide. Technology for GPP continues to evolve. However, tools for analyzing a system of GPP are still inadequate. In this study, a simple analysis tool was designed. The usefulness of this analysis tool is to be able to know the state of the GPP works. This tool will help simulate the conditions that may occur in the plant system. The simulation results will also be known operating conditions that may occur, so the operator can determine what should be done if things happen. Modeling started using Microsoft Excel, which has been equipped with thermodynamic properties. Modeling includes turbine, condenser, cooling tower, and extraction systems non-condensable gas. After validated, the model run simulation in variations that may occur such as decline in the condition of the condenser and cooling tower and environmental conditions, represented by relative humidity. The simulation with variation of condition will decrease the power generated from turbine 3 – 5%.