Based on the measured rainfall data in the Three Gorges reservoir area

this paper investigates the effect of different initial conditions on different types of soil slope stability. A method to reflect the real initial conditions of the water content in the slope is recommended. Unsaturated seepage analysis is adopted to study the effect of antecedent rainfall on different types of soil slope stability. The typical sand and clay slopes are taken as examples to investigate the effect of antecedent rainfall on slope stability. The results indicate that the effect of the initial conditions on different types of soil slope stability can differ considerably. It is recommended that the steady-state seepage field under average annual rainfall can be used as the initial conditions for transient seepage analysis. The lower soil permeability coefficient

the greater impact of antecedent rainfall can on slope stability

and the longer time affected by antecedent rainfall. It is recommended that more than 15 days antecedent rainfall should be considered for sand and clay slopes stability analysis. Furthermore

more computational effort for sand slopes will depend on the 5 days rainfall before these 15 days rainfall. The short term and high density antecedent rainfall has a significant effect on sand slope stability

whereas the long term and low density antecedent rainfall has a significant effect on clay slope. The cumulative antecedent rainfall can be taken as a criterion to determine the minimum factor of safety. For the sand slopes

the time corresponding to the minimum factor of safety matches well with the time corresponding to the maximum 10-day cumulative antecedent rainfall

whereas

for the clay slopes

it matches well with the time corresponding to the maximum 15-day cumulative antecedent rainfall.