Abstract: Based on the shaking table test and the principle of conservation of energy，a series of shaking table tests of slope rock fall are carried out，then the influence laws of collapse distance after instability of the slope under different influence factors including spectrum characteristics，seismic peak ground acceleration，types of site，types of the slope，underground water level and rock fall shape and size are revealed.Finally，critical threshold values of rock fall protection，which uses the probability method and is evaluated by the slope height，under different influencing factors，are put forward.The results show that the distance of rock falls under far field-earthquake is greater than that under the near-field earthquake.The distances of rock falls increase with the increase of peak acceleration.With the increase of height of slope，distance of rock falls in different shapes show increasing trend，while the angle of the slope reaches 60°，the distance of rock falls decrease with the increase of slope angle.The distance of rock falls from largest to smallest are spherical rock falls，cylindrical rock falls，rectangle rock falls and square rock falls considering the influence of peak acceleration of earthquakes，while the distance of rock falls from largest to smallest are spherical rock falls，cylindrical rock falls，square rock falls and rectangle rock falls considering the slope shape.The probability value within the range 1.2H~1.4H (the slope height) reaches maximum based on the probability method，which can provide reference for protection design of structures at the foot of slope.

Key words: Probabilistic method, Shaking table test, Spectrum characteristics, Falling rocks, Earthquake