The expression for the energy of rockburst is derivated based on the Energy Balance Theory. The influencing factors, which accounts for the location,area and the averaged ejection velocity of rock fragments of rockburst zones of underground rockmass are determined quantitatively. It was found that the area of rockburst zones and the averaged ejection velocity of rock fragments decreasing as the increase of lateral pressure coefficient when the ratio of the horizontal stress and vertical stress of surrounding rock is less than 1, otherwise on the contrary. The area of rockburst zones decreases as the increasing diameter of grain of rock, and the ratio of modulus before and after peak loads and density of cracks, fracture toughness of rock, but those increase with the increasing Poisson's ratio. The averaged ejection velocity of rock fragments decreases with the increase of diameter of grain of rock, Poisson's ratio, the ratio of modulus before and after peak loads, but increase with fracture toughness of rock, and increase firstly but then decrease, and towards a fixed value with increasing density of cracks. The proposed approach provides a new idea for the quantitative analysis of rockburst.