Combined Cycle power plants have recently become a serious alternative for standard coal and oil-fired power plants because of their high thermal efficiency, environmentally friendly operation, and short time to construct. The combined cycle plant is an integration of the gas turbine and the steam turbine, combining many of the advantages of the both thermodynamic cycles using a single fuel. The heat recovery steam generator forms the backbone of combined cycle plants, providing the link between the gas turbine and the steam turbine. The performance of the heat recovery steam generator (HRSG) strongly affects the overall performance of a combined cycle power plant. In the present paper performance simulation and exergy analysis of heat recovery steam generator is done to analyze the effects of various design and operating parameters on the performance of combined cycle power plant. For the exergy analysis, the selected objective is the minimization of thermal exergy losses, taking into account the irreversibility due to the temperature difference between the hot and cold streams and pressure loss in the hrsg. Exergy analysis of HRSG is necessary to find out the locations where exergy losses are more and how the irreversibilities will change with various hrsg parameters. The effect of various parameters like pinch point, approach point, steam pressure, steam temperature, mass flow rate of gas and gas temperature are studied on irreversibilities of different sections in HRSG, loss in exhaust gases, mass of steam generated and exergetic efficiency. It is found that selection of pinch point play an important role on the performance of HRSG. Exhaust gas temperature of the turbine and mass flow rate of gas increases the steam production. To reduce the exergy losses the approach point should be as low as possible and the temperature of feed water entering into the economizer should as high as possible. The steam pressure and temperature is selected such that having low latent heat and high quality to get more work.