Abstract: The classic slope stability analysis problem is solved by abandoning the traditional and direct solutions for safety factors of slopes, such as the limit equilibrium equation and the introduction of assumptions. Instead, the general construction method for constructing a slope limit state mechanism is adopted, and the plastic (upper and lower) limit theorems are taken into account. Moreover, taking the interfacial forces and velocities as the main variables and the basic requirements for statically admissible stress field or kinematically admissible displacement field as the constraints, and on the precondition that all assumptions are omitted, the solution for the safety factor problem of slopes is converted into an upper- and lower-bound optimization problem. Furthermore, a complete and united limit analysis method for slope stability is established by gradually shifting the upper- and lower-limit values toward the real solution for the safety factor. To conclude, the proposed method can provide a robust theoretical basis for slope stability analysis due to the omission of assumptions and address the bottleneck resulting from the method of expanding the 2D slope stability analysis to its 3D form. The accuracy and realiability of the calculated results as well as the rationality and feasibility of its engineering applications are validated through 6 representative examples.