This study mainly deals with evaluation of climate change impact on Blue Nile basin cascade reservoir operation i.e Beko Abo,Mandaya and Border reservoirs. To evaluate the impact of climatechange change scenario of evapotranspirations and precipitations developed for three period using output of ECHAM5 with RCM for A1B emission scenario is used to develop future climate change scenario. A hydrological model, HEC HMS, was used in order to simulate the current and future inflow volume to the reservoirs. The projected future climate variable shows an increasing trend for both maximum and minimum temperature and evapotranspiration but precipitation shows fluctuating trend in the next century. Relative to the current condition, the average annual open water evaporation for the three considered reservoir shows increasing trend. Comparison to the base period and the future period average annual inflow volume shows an increase for Beko Abo and Mandaya but Border reservoir shows slightly decreasing trend. A reservoir simulation model, HEC ResSim, was used to simulate the hydropower potential of reservoirs and operation rule curve.