Abstract: In order to measure the dose of pulsed X ray reference radiation field, the theoretical calculation, Monte Carlo simulation and experiment method were used to develop a secondary standard ionization chamber for millisecond pulsed X ray. A pulsed X ray reference radiation field was built based on a millisecond pulsed X ray machine, and pulsed response characteristics experiment of active ionization radiation dosimeter was carried out. From the experimental data, it can be seen that the mainstream active dosimeters currently sold have low pulsed dose response and give false readings, which are not suitable for short pulse and high dose rate of radiation measurement and early warning. They will cause safety trouble to personal, so we should develop active ionization radiation dosimeter suitable for pulsed X ray and popularize pulsed X ray calibration.