Slope is a system with visible uncertainty

illegibility and time-varying characteristics. Safety factor and reliability theory have both advantages and disadvantages in slope stability evaluation. Dual index system is a slope stability comprehensive evaluation system which is established based on a specified index (safe factor) and an uncertain index (reliability). It has both benefits of the indices

and important theory significance and practical value. Considering the interval distribution of material indices and the stable slope's safety factor cannot be less than the critical value

the pure mathematics model is modified. A more realistic dual index system of slope stability is proposed. At the same time

the Monte Carlo simulation method is selected. The dual index system is blent in GeoStudio software. With the help of the powerful computing ability of GeoStudio

a complete and efficient dual index analysis method of slope stability is formed. This method has been applied to analyzing stability of a slope of granite residual soil deposits under rainfall condition. And then some useful conclusions are drawn. It is proved that the method is feasible and efficient.