In this article the issues of sustainability and information value of diagnostic matrix were examined, which are used when it is necessary to determinate the technical condition of constructions. Determination is based on the mathematical instrument of technical diagnostics. One of the most widespread methods of technical diagnostics – a statistical method of Bayes is used. In this article, research of sustainability and informative diagnostic matrix is based on multivariate numerical experiment. Numerical experiment, which consists of a large number of calculations, is performed using software PATC (Probabilistic Analysis of Technical Condition). The analysis is carried out for reinforced concrete floor beams.