For flash-II accelerator a new diode system was developed including a low impedance diode with a flash switch, drift tube, pulsed magnetic system and vacuum target chamber. Its electron beam fluence is three times more than that of the old diode system. By means of decreasing the diameter of cathode, increasing axial magnetic intensity and magnetic lens ratio, and adjusting the distance of flash switch and the pressure of pre-pulse switch a stable working regime of the diode with high fluence electron beam was achieved. While charging 70 kV into Marx generator electron beam of 21.5kJ total energy, spot diameter 52mm and energy fluence 1.01kJ/cm2 on target at a distance 22cm from cathode was acquired.