Abstract：Sliding is a vector concept. The vector analysis method(VAM) of slope and dam foundation stability is put forward on the basis of vector method safety factor. It studies the overall stability of the sliding mass， determines the calculating direction θ according to the tendency direction toward sliding of the whole sliding mass，defines the vector method safety factor F(θ) in terms of the vector characteristics of forces against and driving sliding in θ，and analyzes the stability of slope and dam foundation with F(θ). As the loads and sliding surface of slope and dam foundation are given，the real stress distribution of the sliding surface can be calculated by finite element method. The opposite direction of the sum of the static sliding fractional forces along the sliding surface is θ；and the formula of F(θ) is directly derived from the real stress distribution of the sliding surface and the Mohr-Coulomb criterion，not requiring redundant assumptions. The definition of F(θ) based on the force vector analysis is clear in physics and mechanics. Because the formula of F(θ) is an explicit expression and is simple to calculate，it is convenient to apply VAM to engineering. As a verification，F(θ) is solved by applying VAM to two standard testing slopes of ACADS；and the results are almost the same as those by ACADS. By applying VAM to the dam section #3 foundation stability analysis of the Three Gorges Project，the results are coincident with qualitative analysis—finite element strength reduction method simulating the gradual damaging process of the dam foundation. These case studies show the feasibility and the engineering practicability of VAM.
