Abstarct: Excavation is one of the most sensitive and dangerous steps in construction projects. Lack of accuracy and control of environmental conditions can cause a lot of human and financial losses. Various factors such as soil, geometry, loads, matric suction, etc. affect the stability of the excavations. In this study, the effect of rain as one of the causes of increasing moisture and decreasing matric suction on the stability and deformation of excavation located on the gypsum sandy soil of Najaf, which has a potential for collapsible, has been investigated. For this purpose, three excavations with different heights of 4 meters, 7 meters, and 10 meters under the influence of rain with intensities of 0.5 ks, 0.7 ks, and ks (ks is soil permeability) for 5 days, 7 days, and 10 days are considered. The results show that in all three excavations, the depth of the saturated area increased with increasing time and rainfall intensity, and therefore the slope stability decreased and the displacements increased. At the same rains in low excavation, the decrease in slope stability and the increase in displacement due to the larger saturated area than the unsaturated area, is greater than in deep excavation. The greater the depth of the excavation, the less the effect of rain on changes in slope stability and displacement. According to the considered conditions, the most changes occurred in the 4-meter excavation and rain with ks intensity for 10 days in this study. Slope stability reliability, in this case, decreased by 11.5%, and displacement at zero level increased by 145%. The results also show that in nailling wells, the reduction of slope stability is less than excavation without nail.