With radial slice method

based on the primary assumptions of limit equilibrium method and the mechanism of circular sliding

combining features of radial slice method

the mechanical analysis is conduced to derive a new iterative computational formula of factor of safety（FOS）of soil slope stability

and a new slice method

arc-to-center slice method

is obtained.Based on this method

aprogram is made in FORTRAN language.Through analyzing examples

it shows that the convergence of iterative computation of arc-to-center slice method is fast and stable and both the minimum FOS and critical sliding surface are close to the results of existing methods

which shows the correctness of arc-to-center slice method.Secondly

the influence of the position of normal force between slices on the results of computation is analyzed

which shows the rationality of the assumption that the position of the normal force between slices is at one third of the length of the slice side.