Abstract: Based on the Kelvin viscoelastic model，the dynamic strength of the rock is analyzed theoretically，obtaining the mathematical relationship of rock's dynamic strength and static strength，and also expounding the hardening phenomenon of the rock under dynamic stress.The character of viscoelastic property of rocks determines that the deformation of the rock is not instantaneous but in a gradual process.Under the varying dynamic stress，the deformation of the rock becomes more complex with the time changing，which leads to a big difference between the dynamic strength and the static strength.Based on the dynamic constitutive relationship under the viscoelastic model，and combining with the maximum linear strain failure theory of the rocks，the mathematical relationship between the dynamic strength and the static strength is gradually deduced，and the factors for affecting the effective stress coefficient m are analyzed.Finally，the theoretical results are applied into calculating the dynamic strength of slope rock in Nanshan open-pit mine.

Key words: Dynamic loads, Viscoelastic rock, Strength analysis, Kelvin model