This paper presents the design details and experiment results of a 4 MV facility developed for flash X-ray radiography in Northwest Institute of Nuclear Technology (NINT). The facility is based on the technology of an induction voltage adder (IVA) driving a rod pinch diode (RPD). The facility mainly consists of the prime power source, induction voltage adder, and RPD. The prime power source consists of two 3.2 MV low-inductance Marx generators and four deionized-water coaxial lines. Each Marx generator charges two 6 Ω, 30 ns pulse forming lines (PFLs) in less than 370 ns. There exist two-stage pulse compressions for each pulseline, providing four forward waves with peak voltages of 1 MV at current of 160 kA with a duration time of 60 ns. Four electrically-triggered SF₆ gas switches serve as energy transfer switches from PFLs to outlines, and then four self-breakdown water switch are used to sharpen the risetime and reduce the prepulse. The IVA consists of four-stage induction cavities stacked in series, each of which almost operates at 1.5 MV voltage. A vacuum insulated transmission line (without magnetic insulation) is used for power addition. The RPD is chosen to create X rays through bremsstrahlung. At present, the IVA could produce a 4.3 MV voltage with a risetime (10%－90%) of 21 ns and a FWHM time of 70 ns. The diode current is about 85 kA, and the FWHM time of X rays is about 55 ns. The delay time from Marx trigger to the X-ray output is about 749 ns, with a standard deviation of about 7 ns. With a 2-mm diameter tungsten rod used, the X-ray dose is about 15.5 rad (LiF) at 1 m straight ahead, and the spot size is about 1.4 mm.