Condenser in Steam power plant Block 1 Muara Karang with Surface Condenser type and Water Cooled system, Crossflow with 1 mixed fluid (steam) and other fluid is unmixed (cooling water),water cooled flowing in the tube and steam crossflow directly. Condenser tube often have problems, that is leakage caused by corrosion, bend and dents due to poor heat transfer, even blockage due to marine biota. If there is a leak in the tube, that could cause the risk of sea water in the tube will contaminate the water condensate in hotwell, the result of condensation of the vapor. If contaminated water contents, will damage the components especially in HRSG. To overcome the leaks that occur on the tube then we have to do Plugging,that is the closure of the inlet side and outlet side tube, so that the water doesn't go through the tube. However, due to Plugging, the performance of the condenser is decreased because the surface area for heat transfer is reduced. Therefore, it is important for the amount possibility of Plugging on the condenser tube to keep the condenser performance safe. Condensor performance analysis based on 3 aspect, Effectivenes, Vacuum Pressure, and cooling water flow. The NTU method is used as the effectiveness formula in this study. From the calculations and analysis, it is found that the decrease in effectiveness occurs linearly, where each 5% increase in Plugging occurs average decrease about 2.09% effectiveness at load 3 HRSG (+/- 150 MW), 2.43% decrease effectiveness at load 2 HRSG (+/- 100 MW), and 2.59% decrease effectiveness at load 1 HRSG (+/- 50 MW). Analysis of vacuum condensor obtained Plugging limit is 25.21%.However, based on calculation of the effect of Plugging on the cooling water flow rate, it can be conclude the permitted Plugging is 15% at load 3 HRSG, and 20% at load 2 and 1 HRSG