Indonesian Islamic University (UII) is a private university located in Sleman, Special Region of Yogyakarta. As an educational institution, UII must be able to fulfill the infrastructure to carry out the teaching and learning process for its students, namely the lecture building. At present UII has campuses spread across Kaliurang (integrated campus), Condongcatur (Faculty of Economics), and student parks (Faculty of Law). The process of building a law faculty building UII is on the road Kaliurang km14.5 which is just below the foot of Mount Merapi and has contours of mountainous land. The contours of mountainous land have different levels of land up and down. In mountainous areas can cause problems, namely landslides. In the construction of the UII law faculties building, a suitable slope design is needed, so to solve the problem, slope stability analysis is used. This method is carried out by analyzing the deformation and slope stability by strengthening the geotextiles using the Plaxis 8.2 program. Slope modeling is designed with variations in geometry and variations in water level. Geometry variations used are geometry 70 °, 60 °, and 50 ° while variations in water level with dry water conditions, depth of water conditions 3.8 m, and saturated water conditions. In carrying out the analysis using structural loads and earthquake loads. Deformation analysis is seen from horizontal point X deformation, vertical point X deformation and horizontal deformation of Y-Y pieces. The results of this study are that slope with geotextile reinforcement have large safety factor and small deformations. A more slope geometry variation (50°) result in a larger safety factor and has a small deformation than steep geometry (70°). Groundwater variation have an influence on the results of the safety factor and deformation. The face of saturated ground water has a low safe value and large deformation due to having more water content.