The reliability of power plant and turbine efficiency can work optimally when the pressure in condeser is vacuum. At the same volume, the water will have hundreds of times the mass of water compared to steam so that if the vapor entering the condenser is sprayed water and the vapor turns phase into water, it will occur shrinkage and volume reduction and result in condenser conditions into a vacuum. In fact there is still a gas that can not be condensed in the condenser that is Non Condensable Gas. This will effect on the increase of pressure and vacuum in condenser, hence required Gas Extraction to remove Non Condensable Gas from inside condenser by way of sucked by stem jet ejector. Steam jet ejector serves to suck Non Condensable Gas from the condenser to the intercondenser and aftercondenser to be condensed back so that the gas turns phase into water. This research aims to keep the condenser vacuum in accordance with set points, maintain turbine efficiency, and perform performance calculations of steam jet ejector, analyze difusser pressure and entrainment ratio. Steam jet ejector uses primary steam as a suction fluid using the Bernoulli principle. There are three main parts of steam jet ejector namely nozzle, mixing chamber, and difusser. The pressure of the diffuser on the ejector affects the performance of the steam jet ejector. From the calculation, the increase of entrainment ratio value of 0.12 can increase the efficiency of steam jet ejector by 14%. The entrainment ratio value is influenced by the mass flow rate of the driving velocity and the mass flow rate of the inhaled Non Condensable Gas. The more Non Condensable Gas contained in the condenser will cause the condenser pressure to rise and become away from the vacuum pressure of 0.1 bar. The performance efficiency of the steam jet ejector affects the pressure of the condenser, the efficiency of the 36% steam jet ejector can keep the vacuum pressure in the condenser by 0.12 bar. After the analysis, Heat Exchanger with Plate type is more suitable and effective for use on Steam Turbine compared to Heat Exchangers with Shell and Tube type due to be able to lower the oil temperature up to 10o. Heat Exchanger with Plate type is also more flexible because it can be easily done for addition to its Plate.