Some problems existing in the finite element method for solving safety factor of slope stability
are analyzed. The significance of dilatancy character of rock and soil slope are considered in calculation of safety factor based on the non-associative flow criterion under plane strain condition; the traditional method which overstates or ignores the significance of the rock and soil dilatancy is modified. The results of the example show that the safety factor is increased when the angle of the dilatancy is increased; and the different yield criterions have great effect on the safety factor; the maximum error is to 30 %.