The need for modern science-intensive models for assessing the reliability of building structures, and especially the system "loose body – structure" is now very acute due to the fact that such an assessment has become mandatory in the design. The existing gap is the lack of algorithms for determining the reliability of a complex system and is intended to fill this study. The aim of the article is to develop a method for determining the probability of failure of the system "bulk body – structure" against displacement using the method of statistical tests (Monte Carlo). To determine the probability of stability of the retaining wall against displacement, it is proposed to use the method of statistical tests using the accepted normative method of calculation. According to this method, it is necessary to perform N statistical tests, for each of which we will perform calculations according to the algorithm described in the article. A method for determining the probability of failure of the system "loose body – structure" against the shift by the statistical method of Monte Carlo. A test example was performed in the Mathcad environment. Calculations were performed to determine the probability of failure of the system "loose body – structure" against the shift by the statistical method of Monte Carlo. It was found that the value of the probability of failure of the system "loose body – structure" against the shift over the base service life may be in the range of 1x10-5… 1x10-3. It would also be interesting to use probabilistic methods to develop algorithms for the probability of failure of retaining walls due to loss of bearing capacity of the soil base, strength of the rock base, loss of strength of structural elements and joints, as well as the probability of exceeding the deformation of the base.