Soft and medium-hard rocks are subjected to high rheology under high stress, and they are prone to a relatively large-degree of deformation when perturbed by extal impacting loads. The phenomenon where rock deformation is developed due to extal impacting perturbation in the rheological state is defined as the rock rheological perturbation effect. This work presents a new experimental system for investigating the rock rheological perturbation effect with experiments on medium-hard red sandstone. Results from our analysis show that red sandstone changes under two mechanical mechanisms: deformation-hardening effects at low stress states, and damage-fracture effects at high stress states when impacted by certain extal impacting loads. Red sandstone tested in our experiments has a strain threshold of about 90% of the ultimate strain under the perturbation effect; the red sandstone is sensitive to a perturbed load when its actual strain exceeds the threshold. The perturbed deformation process of the rock can be divided into three phases: decline, approximately constant speed and acceleration. The rock will be rapidly destroyed when the perturbed deformation accumulates to a certain degree. The perturbation effect of rock deformation under uniaxial compression is more obvious than that under axial compression. Based on our experiment, a constitutive relation of the rock rheological perturbation effect is developed.