Limit equilibrium method with horizontal slice method is more suitable for layered soil slopes; but there are some deficiencies than vertical slice method. By studying the relationship of interaction forces between horizontal slice and vertical slice methods

corresponding assumptions of inter-slice forces between horizontal slice and vertical slice methods are established. And a combination model of horizontal slice and oblique slice is adopted when horizontal slice method encounters the sliding surface with toxoplasma. On this basis

the formulas of Sweden method

simplified Bishop method

simplified Janbu method

and Morgenster-Price (M-P) method for calculating factor of safety (FOS) are derived. Among those

two different FOS calculated formulas of Sweden method are obtained according to different satisfied conditions; and the general simplified Janbu method is improved based on previous studies. By using two types of sliding surfaces

arbitrary curve and arc

through analyzing some examples

the treatment of horizontal slice method taken in this article is verified feasible. At the same time

it also shows the results got by two Swedish methods are consistent; and the improved simplified Janbu method is better in analyzing stability of slope than general simplified Janbu method.