The article is devoted to solving the problem of improving the quality of operational diagnostics of the ship main engine in real time. Modern technical diagnostic systems must perform quick and high-quality identification of increasing malfunctions for the most effective use of monitoring results when solving operational tasks with the issuance of recommendations, which will allow expanding the competence of technical personnel in the decision-making process. Therefore, an important task is the development of mathematical models of time series of measured values of controlled parameters, which will allow to improve the procedure of operational diagnostics due to the detection of the probability of failure of ship engine units before the area of the most intense wear or destruction. In order to improve the existing methods of technical diagnostics of technological equipment, effective operational diagnostics algorithms have been developed, which are implemented in software modules and fully take into account technical and economic requirements, stochastic nature of external influences. When building the operational diagnostics algorithms, the specifics of the processes taking place in the ship main engine were taken into account, modern techniques and methods of mathematical modeling and information theory were used. On the basis of the values obtained as a result of measurements of the controlled parameters of the ship main engine, autoregressive models of the moving average were selected, which describe the obtained time series as accurately as possible. The parameters of the autoregression models were identified using the method of least squares. A method of operational diagnostics based on the determination of spectral entropy and the procedure of logical-time processing is proposed. On the basis of the developed mathematical models and the proposed diagnostic method, an automated system of operational diagnostics of the state of the ship main engine has been developed, which allows timely detection of critical modes of operation of technological equipment in real time.