There are two kinds of definitions for safety factors based on strength parameters of c tan(Definition 1) and geotechnical parameters of a, k(Definition 2) in limit equilibrium analysis with dual safety factors. The influence of different definitions on the calculation of slope safety factors is analyzed with strength dual reduction finite element method(FEM). It is shown that the safety factors are different in two kinds of definitions while the reduction rates of strength parameters(c tan) and geotechnical parameters(a, k) are in same proportion. The different DP yield criteria are related to the parameters of a and k. If circumcircle DP yield criterion is adapted, the safety factors with Definition 1 are approximate to the ones with Definition 2 on all kinds of soil slope. And if DP yield criteria of the plane strain matching and criteria of homalographic circle are adapted, the safety factors are slightly lower with Definition 2 than those with Definition 1 for clay slope and much lower for landslide zone or slip with rough broken stone