For the purpose of trying to find a reasonable criterion for stability analysis of three-dimensional slope based on strength reduction method

the displacement mutation criterion and the connectivity criterion of plastic zone are analyzed based on Zhenzhuba slope by FLAC3D; and then the results are compared with the ANSYS and two-dimensional limit equilibrium’s ones. It is shown that

in the stability analysis of three-dimensional slope using strength reduction

mutations are easily identified in the curve between the increments of total displacement and reduction factors and reasonable feature points should be selected on the top of the slope for the displacement mutation criterion. Meanwhile

a modified criterion is put forward due to the shortcomings of the connectivity of plastic zone criterion. It is that the mutations

which are on the curve between the increments of penetration rate of the plastic zone and reduction factors

are used to judge the instability state of three-dimensional slope. So the reasonable choice of three-dimensional slope’s instability criterion should be as follows. If the slip band is known clearly

the increments of penetration rate of the plastic zone criterion is suggested; if not

the displacement increment mutation criterion is suggested.