In order to study the relationship between safety factor of slope and its slip plane during the slope stability calculation by strength reduction method

the theoretical deduction and numerical calculation of strength reduction method by FLAC3D are done. The safety factor and location of slip plane for slope are analyzed for a homogeneous slope with the variation of cohesion and friction angle . The analysis results show that (1) the safety factor of slope is influenced by anyone of cohesion and friction angle

but the location of slip plane is instead influenced by the combination function of c and φ

which has the formula of

where is the height of slope; (2) when equals to a constant

the locations of slip plane will not change by the variation of shear parameters and ; with the increase of

the failure mode of slope changes from shallow slippage to deep slippage

the slip plane becomes more and more smooth while the top of it moves farther away from the vertex of slope

and slipping volume becomes greater.