In this paper a thermoeconomic and exergy analysis of a steam power plant located at Villa de Reyes, México is presented. This study is focused on the analysis on partial load of this plant. According to the steam power plant operation manual this plant is able to operate at 25%, 50%, 75% and 100% of the total load installed, and some design parameters are established for this operation loads. Nevertheless during this study it was observed that this parameters and operation loads conditions are not the most efficient from the energetic and exergetic point of view, and also, the values of the thermal parameters used for these operation loads were not the optimum. In this context the objective of this research was to design a model for the power plant simulation in order to determine the best design parameters and operation loads conditions for this particular facility. First of all the model was validated, with the information of the operation manual of the steam generator. Once the model was validated, it was achieved the thermal, exergetic and thermoeconomic analysis. As a result it was observed that the best operation load conditions are at 100%, 98.4%, 93.3% and 75.6%. Also some optimal values of air-gas relation, extraction pressure and drum pressure were found. It was observed that an energetic efficiency up to 35.5% and exergetic efficiency up to 29% may be achieved. Finally it was achieved the thermoeconomic analysis in order to determine the cost of the energetic and exergetic loses and identify the elements that produce the higher irreversibility.