In the present investigation, a simulation model of the thermal calculation of the steam generator's steam generator 350 MW, operating under a Rankine cycle with superheat and regeneration, was developed. An analysis was carried out, modifying some parameters of the combustion (air and fuel flow) and the temperatures reached by the products of the combustion at the exit of the steam generator's home were determined, using the method of successive substitutions, applied to the thermal calculation methodology, with a stopping criterion of the approximate relative error of ε_ra <1 x10-8. It was found that the temperatures reached by the combustion gases at the steam generator's outlet for the 100%, 75%, 50% and 25% regimes are: 1492.4 ° C, 1379.3 ° C, 1238.0 ° C and 980.0 ° C, respectively. Regarding the effect of air dosing on the thermal efficiency of the cycle, it is observed that it increases slightly with the increase of the dosage. Being the maximum thermal efficiency of the cycle of 35.8%