Abstract: The surrounding rock structure of roadways with low-stiffness roof and coal seam exhibits high rock burst risk, where roof lithology and thickness are key factors governing structural stiffness. To clarify the influence of roof rock stiffness on coal burst failure, uniaxial compression tests were performed on coal-rock composite specimens with different stiffness ratios. Using the fragment ejection kinetic energy test method, the deformation rebound, unloading energy release characteristics of rock, and the ejection law of coal fragments in composite specimens were investigated. A mechanical model for deformation rebound of unloading rock was established, and the differential effects of rock lithology and height on the dynamic failure behavior of composite specimens were analyzed. Results indicate that as the rock stiffness of composite specimens decreases, both the deformation rebound velocity and releasable elastic energy of rock increase, accompanied by an extended ejection distance of coal fragments and more prominent dynamic failure characteristics. The extreme value of rock deformation rebound velocity and the ejection kinetic energy of coal fragments both show a negative power function correlation with rock stiffness. The ejection kinetic energy of coal fragments in red sandstone-coal composite specimens is 2.78 times that in granite-coal composite specimens, and the fragments ejection kinetic energy in 180 mm-high white sandstone-coal composite specimens is 2.13 times that in 40 mm-high counterparts. As parameters influencing rock stiffness, lithology has a greater impact on the dynamic failure behavior of composite specimens than height. Thus, under the same roof stiffness, coal ribs under hard and thick roofs have higher rock burst risk than those under soft and thin roofs, making them key targets for prevention and control.