In our time The power system unite into the United power systems, this helps them to fulfill their main function, namely - to supply users with energy, but there is a risk of the reliability of power system. So that the power system could fulfill its functions, are advanced requirements on the reliability, which must be observed In order to estimate the stability of power system and subsequently, if it is necessary to take correct measures, power system studies as mathematical model. One of the existing programs, in which it is convenient to examine the proceeding processes into] of steady, emergency and other states, they developed in France. Program EUROSTAG is convenient for the analyzes of the results, since it allows their two forms - as the table and of the graphs. With the graphs it is possible to reflect changes of the parameters both separately in each unit of system and after combining the parameters.