To solve the problem of safety of mechanical systems, it is necessary to calculate the indicators of their achievement of the limit state on the determining parameters of operation in the normal and emergency situations. Degradation processes that cause a decrease in strength characteristics, formation and growth of cracks, are considered. They require the creation of models of damage accumulation under different operating conditions for assessment of the technical condition, residual life and record for the importance of various operational factors. It is assumed that the speed of the process of damage accumulation by the mechanical system corresponds to the beginning of some period of time and depends on the technical condition of the system at the beginning of this time period, its properties and parameters of the external effects. Efficiency with a given probability characterizes the life of the mechanical system. Joint effect on the accumulation of damages of dynamic loading, friction and related to them wear processes is considered in the article. Computer modeling of dynamics and wear of nodes allowed to tie together the change of functional and dynamic parameters of the machines with wear of individual elements and to predict these processes for the time of future operation. The change in the dynamics of the mechanism due to wear leads to a further increase in the intensity of wear of the conjugate elements, and as a result, an increase in the probability of failure. The model is considered concerning the assessment of technical condition of the elements of mechanical system, that takes into account the dynamic loading and wear, which allows to carry out the refined calculations on the assessment of probability of the parts breakdown. As an example of using the proposed approach, the results are presented, which are related to calculating the probability of breakdown of the connecting rods of the opposed compressor under the combined action of cyclic loading and wear. It is shown that the probability of breakdown of the compressor rods at nominal (load 250 kN) modes of its operation increases from 0.074 to 3,363 with an increase in the coupling gap due to wear in the studied range from 0.05 to 0.15 mm. It is noted that the proposed method allows to take into consideration the effect on the life duration and reliability of mechanical systems of wear and possible overloads.