The article presents a basic formula and a universal table for development of structure functional models of big technical systems. The method takes into account priorities of performed functions and substructures of big technical systems, also, maximum and minimum values of basic indices of technical systems. In order to compare “ideal” and real models it is recommended to use a corresponding subtraction of matrixes of quality indices. For this purpose, matrixes of indices are sorted into two groups: the one, where the minimum value of an index is considered the best, and another, where the maximum value is considered the best. The results of matrixes subtraction make a basis for the rules of models comparison. The article demonstrates a specifically designed table for processing of the results of matrixes subtraction and calculation formulas of standardized weighting coefficients of importance for each index and a complex quality index of maintenance of the assessed systems. It also contains rules of making ratings of systems’ quality. The main positive effect from the application of the proposed method is a considerable decrease of time and resources needed for the quality assessment of systems and a possibility of software realization of a rational processing of information in the process of management of big technical systems’ maintenance.