The 200 keV X-ray pulser has a good surface density resolution when being used in the imaging diagnosis of high speed and low density regions in ejecta. Heuce it has become one of the important technical diagnostics methods of ejecta. This papper develops a 200 keV pulse driver based on the PFN-Marx technology. Using a pre-trigger method, the 200 kV pulse of a 62 ns width and a 25 ns rise time is produced on the 40 Ω water resistance, A “Washer-Needle” type diode which can work under 200 kV voltage is also designed. When the diode operating voltage is 210 kV, the pulser outputs the X-ray pulse of a 40 ns width, a 1.2 mm spot size and a 15 mR dose at 1 m distance .