Introduction  Cycle load has effect on the rock strength and mechanical characteristics and China still lack the research on dynamic characteristic parameter of mechanism of medium weathering sandstone.

  Method  According to test physical parameters of 90 medium weathering sandstones, the deep and velocity of sonic were presented as power founction, then MTS machine was used to conduct cyclic load test in different amplitude obtain the sample′s law of hysteretic cycle, dynamic elastic modulus, axial strain and damping ratio in axial cyclic load.

  Result  The results show that the velocity is increasing with the increasing of the depth. The density of sample approximate 2.50 g/cm³. The axial strain and plastic displacement are increasing with the increasing of rounds. The increasing area of hysteretic cycle means that rock inner cracks is creating continuously resulting to increasing consumption of energy.The form of hysteretic cycle is same as sharp leaf and what it′s sharp but not around in the time of increasing stress or decreasing stress means that the sample reflection of changing stress is rapid and the plastic displacement in the time of changing stress is little relatively. The dynamic elastic modulus is increasing and damping ratio is decreasing with the increasing of dynamic strain. The math relations between either elastic modulus or damping and dynamic strain is presented as linear. The correlation coefficient R² is almost above 0.85 showing good relevance.

  Conclusion  This work provides some guidance for further study on testing and evaluation of dynamic characteristic parameters for soft rock foundation of nuclear power plant.