The present research program deals with the repowering of existing steam power plants. which is one of the topics of the roadmap to increase the efficiency of thermal power plants in the country. Repowering is done by adding one or more gas turbines to the steam power plant cycle. Other goals of repowering include increasing the production capacity and useful life of the power plant. Repowering of steam power plants includes full and partial repowering methods. Types of partial repowering methods include parallel or auxiliary boiler repowering. feed water heating repowering. and hot air box repowering. Each of these methods has its own characteristics that have advantages and disadvantages. In this dissertation. first. various repowering methods are studied. then. by performing software simulation of the thermal cycle of the sample power plant. Shahid Mohammad Montazeri Power Plant. the energy and exergy of the existing cycle are analyzed. and then while simulating and analyzing several repowering method The results obtained are expressed. Energy and exergy efficiencies are considered as objective functions and finally the results are compared. Cycle Tempo software was used in the simulations. The thermal efficiency of the existing cycle of the target power plant was calculated to be 34.8%. After simulation. the efficiency of the new repowered cycle by the heating water heating method was 38.38%. the auxiliary boiler rehabilitation method was 47.3% and the complete repowering method was 49.8%. Come. Keywords : Increased efficiency. Exergy efficiency. Repowering. Thermal power plant. Full repowering. Parallel repowering. Hot air repowering. Parallel repowering. Cycle Tempo. Mohammad Montazeri power plant.