The dynamic characteristics of nozzles are of critical significance to the combustion stability of liquid rocket engines. However， the lack of efficient external periodic flow pulsator， particularly in the environment of high back pressure， increases the difficulty in generating pressure and flow pulsation with strong amplitude of pipeline incoming flow. To solve these problems， a flow pulsator is developed using inertia drive to generate strong sinusoidal signals which can generate pressure amplitude up to 15% in a high back pressure environment. The flow pulsation was obtained by measuring the liquid film thickness of the swirl injector with the conductance method. The dynamic characteristics of the swirl injector at different pulsation frequencies were experimentally studied under the conditions of 0.5， 1.0 and 1.5 MPa， respectively. The results show that the increase of the back pressure has an inhibitory effect on the flow pulsation of the swirl injector. The pulsating velocity fields in different back pressure environments were obtained by cross-correlation processing of continuous spray images， and the results reveal a decreasing trend of the amplitude of the spray velocity transfer function with the increase of ambient pressure， consistent with the influence rule of back pressure on the nozzle transfer function.