A 156MW steam cycle power plant has been chosen as a case study. Two repowering scenarios have been utilized for this case. Thermodynamics code has been supplied for combined cycle and STIG combined cycle and compare with each others. The exergy and exergoeconomic analysis method was applied in order to evaluate the proposed repowered plant. Also; computer code has been developed for exergy and exergoeconomic analysis. It is anticipated that the results provide insights useful to designers into the relations between the thermodynamic losses and capital costs; it also helps to demonstrate the merits of second law analysis over the more conventional first law analysis techniques.The efficiency of the STIG repowered plant compares favourably with repowered combined cycle.