Single safety factors are used for most stability assessments of tailings slopes which can not reflect the whole evolutions of stabilities of tailings slopes subjected to variations of external condition. A method of time-varying analysis of tailings slopes was proposed to solve this problem and the time-history of safety factor was used to evaluate the stabilities of tailings slopes. A time-varying model was established to analyze a tailings pond. Conditions of rainfall infiltration

water level fluctuation and the associative action of both of them were simulated by numerical method to study the variation of safety factor with time. The results show that after 6 hours the rates of decrease in safety factor under different rainfall intensities are similar. But within 6 hours the greater the rainfall intensity is

the faster it decreases safety factor. The rain types will affect the trajectory of the variation of the safety factor; and the constant rain which is widely studied is not the most critical rain type. The variation of the safety factor lags behind the water level fluctuation. And the hysteretic effect is weakened by the declination of rising rate

the increasing of descending rate and the decreasing of the varying range of the water level. It is of important significance for the designation and operation of tailings ponds.