A multi-pulse X-ray radiography system, based on an RF linear accelerator, was suggested to be employed in diagnosis for hydrodynamic test. The system can provide several interval-adjustable electron pulses, with pulse widths of tens to a hundred nanoseconds and beam transverse size （FWHM） less than 1 mm, within a duration of 10 μs. We used Monte Carlo codes, Geant4, to simulate bremsstrahlung characteristics, such as exposure dose, energy deposit in target and increment of X-ray spot size by electron scatter, of 30 MeV electron beams bombarding tantalum target with various thickness in a certain radiography layout. Simulation results show that the exposure dose at 1 m away from the target right ahead was about 9.1 R and the X-ray spot sizes were not increased obviously with the thickness increment. The pulse number was limited by temperature rise in target, which was increased intensely with a very tiny beam transverse size. The rotating target could be employed to break the limitation of pulse number, but the pulse interval was limited by decrement of yield strength with the rise of target temperature.