Abstract: The traditional method with a single factor assumed in the three elements of the interslice force is abandoned, and the full elements of the interslice force are rearranged. The orthogonal force at the curature center of bottom midpoint of ship circle is equivalent to substitute the interslice force. The equivalent interslice force systems are established. From three basic balance equations, a limit balance formula is established, and a simple expression for interslice force function is proposed. A simple expression for vertical slice method for safety factor of slope stability similar to the Sweden method is obtained. This method is applicable to arbitrary slip surface. The formula for safety factor of stability and inter slice force are simple. Its operation and calculation are as simple as the Swedish method. Its accuracy is consistent with those of various high-precision methods. It does not need a trial and has no failure situation because of no convergence condition and is easy to compute in excel. The computed results of an example are compared with those by various traditional methods of Lossap2009.