Abstract: FLASH II accelerator is a low impedance relativistic electron beam accelerator for the nuclear weapons effects simulations. The accelerator system consists of a Marx generator, a water-dielectric coaxial line, a diode and more then ten auxiliary equipments.This paper concentrates on the accelerator construction, machine adjustment and parameter measurements. The results of test running at DC charge voltages of±55kV and ±70kV are presented. At present,the diode output voltage is 1.2MV with ur rent 600kA.The accelerator is now used for physical research programs.