Abstract: Based on the influence of excavation and creep degradation on the stability of high slopes in open-pit, a stability model of slopes in life-cycle is proposed. By introducing the deterioration theory of rock strength, the calculation formula of safety factor under time effect is derived. Considering the prestress loss of anchor cable and the creep phenomenon of slope, the expression of safety factor of creep slope under prestress loss condition is established. Forthemore, the influence law of time factor of slope and prestress loss of anchor cable on slope is discussed. Taking Dagushan Xijing slope as an example, the decay theory is embedded into the strength reduction method with the help of the flash language built in the FLAC^3D, and the improved strength reduction method is used to calculate the time-dependent safety factor of the slope. The results show that the "L" shaped deterioration of rock strength over time makes the factor of safety for creeping slopes lower than for excavation only, which is more consistent with the actual engineering. The reinforced slope still has the risk of instability due to the prestress loss of anchor cable. Four kinds of reinforcement control schemes of anchor cable are compared and selected, on the premise of meeting the safety production in the whole life cycle, the scheme with the best economic benefit is obtained.