Abstract: To restrain the space charge effects causing severe broadening of an ultra-short electron pulse with high charge density, a novel method is proposed based on a compensating element. The element is an axisymmetric cylindrical cavity, of which the side wall and a fine mesh end face through which the electron pulse can get out are both grounded. The permittivity distribution of the other end face in which there is an entrance pinhole is so developed that the specific potential distribution can be formed when positive potential is applied to the conducting layer inside the pinhole. The correspondingly formed inner electric field can exert different electric force on electrons of different position, which is opposite to that of space charge effects, and eventually restrain the unwelcome electro