Abstarct: The occurrence of a variety of failures in a flexible pavement system accounts for a major part of maintenance costs, so that pavement designers fail to deal with the downtime of the pavement, used failures as a pavement response directly in design. It is possible to improve the design method if failure causes by incorrect design. Basically, the occurrence of a failure is a random phenomenon; therefore, a random phenomenon is investigated through probable methods. The main focus of this research is the reliability method that used as a new method that has changed most of the regulations in recent decades. Also due to the limited possibilities of this research, only rutting was considered for reliability evaluation methods. In this research, field observations is used. For this purpose, a road axis is selected and the parameters of the input design of the pavement, such as load, climate conditions, conditions of construction and implementation, drainage conditions and material properties, are constant, The rut depth as a rutting intensity index, in Speed, slow lines, and in sections of pavement with one to four years old AC overlay is taken. The analyzes were carried out in four stages. Descxriptive statistics analysis in the first stage, goodness of fit analysis to find data distribution in the second stage and in the third stage, after the definition of limit states, reliability analysis was performed. Two limit states are defined baxsed on the average intensity and high intensity of the rut depth. The results of reliability analysis are effective in determining the exact time of rutting. In the final stage of the analysis of this research was to investigate the uncertainty of rutting reliability index with the Monte Carlo simulation method. The simulation results showed that the reliability analysis performed are correct. At the end of the study, a probabilistic model is introduced that predicts the growth of the rut in the coming years.