Present methods for forecasting and evaluation of thermal power plants reliability were based on appliance of statistics and probability calcu lation related to strength and in the same time lean ing on modern methods for deterministic project-constructive calculations of elements, subsystems and systems. Applying the advantages of modern directions in system reengineering and structural or RCM (Reliability Centered Maintenance) way of using the best methods in reliability analysis of complex systems, the block diagram of mod ified method for basis referential 300 MW block has been created. As a starting database, the results of research of basic configurations of thermal power p lants for solid fuel "Ug ljev ik" and "Gacko" with nominal referential power of 300 MW were used. For other facilities inside thermal power p lants witch no minal power differs fro m 300 MW, recalcu lation of reliability indicators has to be carried out. Whereat the simple emp irical relation in dependence of previously determined reliability indicator for 300 MW system is used so as the exponent determined on basis of statistical data processing from the exp loitation during the lifespan of the power plant. The method is of the iterative nature and is about to be terminated as the starting hypothesis related to matching of results of the forecasting and real exploitation results affirms. The research related for suggested modified method gave several relat ively new results which are presented inside the paper. The result represents the algorithm of modified method for evaluation of reliability of referential thermal power plant system and its modificat ion aiming to include thermal power plants of other nominal powers.