Abstract: In order to research the influence of size effect on bump- prone test results, laboratory uniaxial compressive strength tests and numerical simulations we re applied to analyze different size specimens which the ratio of height and diameter was same and the interval of diameter was between 25 ~ 75 mm. The results show ed that the smaller size specimenDs compressive strength was low. The acoustic emission happened early with a great quantities. The energy accumulated before peak point was low, and the energy released slowly. The specimenDs failure form was plastic and splitting. The impact energy index was low, and the smaller size specimen had weak bump- prone. The bigger size specimen口s compressive strength was big, and the acoustic emission concentrated around the failure point. The energy accum ulated before peak point was high, and the energy released rapidly. The specimenDs failure form was brittle and shearing. The impact energy index was high, and the b igger size specimen had strong bump- prone. A modified coefficient of the impact energy index in different diameters specimens was obtained, and the influence of the size effect on bump- prone testing result was decreased.