The strength reduction method is widely used for slope stability analysis

and different instability criteria have their own characteristics. Among them

a simple and practical one is the mutation in the displacement reduction coefficient curve. This study uses cluster analysis to select the displacement mutation feature point

and identifies its mutation using the self-organizing neural network change point analysis method. Then

we suggest an improved criterion for this mutation. Such a fusion method－that clusters such an analysis－is more objective and mathematically based. For typical examples

safety factors calculated by this analysis method are closer to the judging values than those of the strength reduction method built in FLAC3D.