The yield criterion parameters of the soil material change with different values of the cohesion and the angle of friction because of sustained rainfall infiltration. Based on the Mohr-Coulomb(M-C) and Drucker-Prager(D-P) yield criteria, some reasonable yield criteria selections were discussed for quantitative analysis of unsaturated soil slope stability. Moreover, a critical point was found at the effective angle of friction equaling to 16.5° by transformation of parameters related to unsaturated soil under sustained rainfall. When the effective angle of friction more than 16.5° through parameter transformation of different yield criteria under natural condition, the calculation result of the safety factor was such that: f(DP1) > f(M-C) > f(equivalent M-C) > f(DP2) > f(DP3). While the effective angle of friction less than 16.5°, through parameter transformation, the safety factors were in the following order: f(DP1) > f(M-C) > f(DP2) > f(equivalent M-C) > f(DP3). The calculated results from a case study showed that the equivalent M-C yield criterion should be the best at evaluating soil slope stability before rainfall; the DP2 yield criterion should be selected to calculate the soil slope stability at the effective angle of friction less than 16.5° under sustained rainfall. The yield criterion should be selected or adjusted reasonably to calculate the safety factor of unsaturated soil slopes before and during sustained rainfall. Based on the Mohr-Coulomb (MC) and Drucker-Prager (DP) yield criteria, some reasonable yield criteria selections was discussed for quantitative analysis of unsaturated soil slope stability. Moreover, a critical point was found at the effective angle of friction equaling to 16.5 ° by transformation of parameters related to unsaturated soil under sustained rainfall. When the effective angle of friction more than 16.5 ° through parameter transformation of different yield criteria under such condition that the calculation result of the safety factor was such that: f (DP1)> f (MC)> f (equivalent MC)> f (DP2)> f effective angle of friction less than 16.5 °, through parameter transformation, the safety factors were in the following order: f (DP1)> f (MC)> f (DP2)> f (equivalent MC)> f res ults from a case study showed that the equivalent MC yield criterion should be the best at evaluating at a soil slope stability at the evaluating at least 16.5 ° under sustained rainfall The yield criterion should be selected or adjusted reasonably to calculate the safety factor of unsaturated soil slopes before and during sustained rainfall.