Traditional limit equilibrium methods of slope stability fails to consider the influence of soil strength indexes variability. Based on probability analysis principle of limit state, Monte-Carlo method is used to calculate the reliability of stability of homogeneous embankment slope. And with constant safety coefficient, changes of slope failure possibility with different levels of soil strength indexes are studied. The corresponding relationship between safety coefficient and reliability index of the slope and changes of safety factor with variation levels of soil strength indexes are analyzed. Results show that: the slope reliability is affected by soil strength indexes variability significantly, indicating sharp decreases with increase of soil strength indexes variation levels; in order to get the slope the identical reliability, safety coefficient should be changed according to soil strength indexes variability. The safety coefficient should be changed according to reliability index and soil strength indexes variation levels and based on which three parameters function is put forward.