Despite the long operating experience with steam power units in the Electric Power System of Serbia (out of which some are at the end of or had even passed their planned working lives), unfortunately, there is a lack of data for their operating regimes, process parameters and performance deviations, the economy and operating states for the previous period. These data would not only be useful for optimal process control, but also for the planning of maintenance, retrofits and repowering of power plants. For these and other equally important reasons, the software system for the diagnosis of operating conditions, control of economy and operating states of different components has been developed for the referential steam power unit. A better control of the process and operating state, thanks to the use of the results obtained with this software system, will bring a lasting benefit to the efficiency and economy increase. Furthermore, it will enable an increase of reliability and availability of steam turbine units and make their working life longer. The basic characteristics of this software system and some of the results obtained by its testing using the available data base for referential unit operation are presented in this paper. (c) 2010 Elsevier Ltd. All rights reserved.