Abstract: The electron beam generated by the Dragon-Ⅰ linear induction accelerator strikes the bremsstrahlung converter target to generate X-ray and causes tantalum target damage and hydrodynamic expansion, which results in target density decreasing for successive pulses. The time varying target density was measured by applying a low energy X-ray with energy about 450 keV and spot diameter of 1 to 4 mm along with an intensified charge coupled derice(ICCD) camera. The experiment results show that the target density is basically unchanged for 1 μs after beam-target interaction, and no particle ejected from the front side of the target is found at the same time.