It is common to simplify some calculation conditions when applying slice method to calculate the factor of safety of a slope.In this paper

the influences of the simplification of slice gravity center and seismic load imposition on the factor of safety are discussed by several design projects via the Bishop method.The applied direction of vertical seismic load is also considered.The results show that:（1）The influence of the simplification of slice gravity center on safety factor can be neglected.（2）When considering the simplification of the imposition of seismic load

the deviation generally decreases with slope ratio reducing and central angle increasing of the slip surface.On the contrary

the increase of the height of the slope and the design earthquake intensity has negative effects on the deviation.Besides

the variation of cohesion and internal frictional angle has little influence on deviation.（3）The selection of vertical seismic force direction mainly depends on designed seismic intensity.The slope height further affects the critical parameter values of direction changing at the same earthquake intensity level.