Reliability analysis has gained special importance in geotechnical engineering in the past decades.One of the most important fields of geotechnical issues is the slopes stability. Slope stabilityanalysis and their reliability analysis
against slip and loading are important. Geotechnicalengineers are also interested in improving and reinforcing weak slopes and increasing their factorof safety and reliability index. In this study, the uncertainties in soil strength parameters such ascohesion, internal friction angle and unit weight and force created in geogrid layers due to pull-outand bonding between soil and geogrid are considered. Then using Monte Carlo simulationDepending on the height of the slope, the reliability index is obtained in both of unreinforced andreinforced states. The critical slip surface of slope failure is also determined using PSO. Theresults of this analysis indicate the important role of reinforcements in increasing the reliability ofsoil slopes..