Under a certain electric field strength of steep pulse, plenty of micropores occur in the cell membrane. The number and diameter of micropore increase rapidly with the increase of electric field strength, the membrane breaks and the cell dies at last. This phenomenon is called as irreversible electrical breakdown (IREB). To research IREB of tumor cell, integrated with power electronics and conventional high voltage pulse generator, an energy-controllable steep pulse apparatus for tumor treatment is developed. The peak value, width, frequency and rise time of the output pulse can be adjusted independently, so the energy of the output pulse can be easily controlled. The apparatus is applied in cell experiment after a detailed analysis of its operating principle and debugging in laboratory. The experiment results show that the device works steadily and satisfies the demand of medical experiment.