In order to find the effect of the ignition composition amount on the short impulsive thruster and select the right ignition composition amount,the simulated test device was used and the p-t curves were obtained. Results show that the ignition delayed time changes from 1.48 ms to 1.06 ms,and the pressure increasing time changes from 0.37 ms to 0.16 ms,and the action time is about 1 ms. It indicates that the ignition delayed time and the pressure increasing time can be shortened if the ignition composition amount is increased. The ignition composition amount of 80 mg is selected to meet the target requirements.