Abstract: The Sarma method is widely used to calculate the slope and embankment stability analysis.But the method assumes the horizontal direction as seismic force direction.So it does not consider the impact of the different directions of seismic force.In order to study the critical seismic coefficient and stability factor in different directions under the distribution of seismic forces,this paper,based on the traditional Sarma,assumes that non-horizontal seismic force,at any given positions of seismic force,and try to derive the formula.And the mean value is introduced to iteration when deal with the result of critical seismic coefficient.Examples are used to show the relationship among the directions of seismic force and the slope stability factor.After solving the minimum critical seismic coefficient,the represent angle of the minimum critical seismic coefficient is the angle of the smallest seismic force.On this point of the smallest seismic force,the stability analysis is gained in two classical examples.The analyses of the two examples derive the minimum value at last.Through the analysis,on the one hand,the direction of seismic forces represented by the minimum value is not necessarily pointing the outside horizontal direction.On the other hand,the corrected minimum critical seismic coefficient represents the authentic status that the smallest seismic force can be withstood by slope.Last but not the least,there is no sharp contrast between the calculated slope stability factor and the original slope stability factor.That is to say,when assuming the direction of seismic force,there will be no inaccuracy of assuming any position of the seismic force to calculate the valid slope stability factor.