The original numerical manifold method (NMM) is extended for stability analysis of a toppling slope with complex sliding surface and cohesion and tensile strengths existing in discontinuities. The extended NMM is shown effective by reproducing a centrifuge test. With NMM simulation, the commonly used Goodman and Bray's analytical method is shown adaptable to a toppling slope model with a simple sliding surface without cohesion and tensile strengths in the discontinuities. It is shown that the deformation of the sliding body has no significant effect on the result. The relationship between dip angle and critical friction angle is investigated. A real toppling slope is simulated and the necessary cohesion and friction angle are verified.