The geosynthetic composite lining system composed of a membrane layer at the bottom of a tailings pond often forms a weak layer that threatens the stability of the dam body,thus requires special attention in the analysis. This article is based on the hydraulic analysis system Autobank to mark the weak layer of the lining formed by the film laying surface. If the search for the most dangerous sliding surface intersects with the weak layer of the lining, a composite sliding surface composed of the weak layer of the lining and some arcs is added. The calculation method adopts the Morgenstern method applicable to various shapes of sliding surfaces to obtain the minimum anti sliding stability safety factor of the storage body. The analysis of calculation examples considering different positions of membrane laying shows that the safety factor of the composite sliding surface partially passing through the weak layer of the geotechnical lining is relatively small, and this translational sliding is completely possible,making it the most dangerous sliding surface in this section. The results of this article can provide scientific basis for the design and operation of tailings ponds,and provide references for similar projects.