The aim of this study is to show the effect of live steam parameters on thermal and exergy efficiencies of thermal power plants under various load condition. Soma Thermal Power Plant (Base Case) is operated under sub-critical conditions has single reheat stage and six regenerative heaters. Live steam conditions of Base Case are 139,2 bar and 540 degrees C, and the temperature of reheat steam is 540 degrees C. Case 4 is found the best system configuration in terms of performance. Optimized ultra-supercritical thermal power plant (Case 4) consists of double reheat, ten regenerative heaters, two depsuperheaters and a regenerative turbine. Live steam conditions of this system are taken as 300 bar, 600 degrees C and its reheat steams are heated to 620 degrees C. Simulations are carried out by the Ebsilon Professional software. Finally, the results of analysis are compared to that of Base Case. Thermal efficiency and exergy efficiency of ultra-supercritical power plant (Case 4) are increased 9,24% and 8,06% under 100% load condition, respectively. Furthermore, CO2 emission drops 3.384.916 tonnes/year under 100 degrees/0 load condition. The results of this study show that live steam parameters have a huge impact at efficiencies under various load conditions.