The paper presents a stability analysis of a municipal waste landfill lined by a single-drainage and mixed sealing layer. The drainage layer is medium-dense sand, while the mixed sealing layer consists of compacted stiff highly plastic clay and a synthetic barrier in the form of a double-sided textured HDPE geomembrane. Beneath a sealing, there is a non-woven geotextile with drainage and protective functions. The landfill was assumed as a sub-level in the excavation, where the maximum height of the waste is equal to the height of the excavation slope. Variable geometrical parameters of the municipal landfill were assumed, such as the height, the width and the inclination of the waste body. The structure stability analysis was performed using the GEO5 numerical programme. The calculations were carried out several times, looking for the most unfavourable slope surface. The considerations were conducted for checking the state of equilibrium (stability) according to design approach 3 (DA3) of Eurocode 7, approved according to the Polish National Annex and accepted in most CEN countries, and according to approach 1 (DA1) and 2 (DA2) adopted in other CEN countries. The values of the degree of utilization (utilization factor) for the ultimate limit state GEO according to Eurocode 7 were given. Stability calculations were also made considering the values of safety factors, i.e., using the characteristic values of parameters and actions. The values of the utilization factors achieved in all design approaches and the safety factor were compared.