The underwater performance characteristics of solid rocket motors (SRM) are different from those in the air as they are surrounded with high density medium water. In order to have a deep understanding into the performance characteristics of underwater SRM

the impact of the change of the flow structure on thrust was analyzed. A 2D axial symmetry model was adopted to simulate underwater SRM in different working conditions

and the figures of thrust oscillations were obtained. After analyzing the changes of thrust in different stages

the relationship of thrust peak value and neck breaking was studied

and the thrust oscillation amplitude and frequency changing with working environment were studied. The research results show that the thrust oscillation occurs due to the periodic neck breaking induced by the shock wave. In addition

as a result of the action of gas bulge and backattack

the jet thrust takes on a multistage frequency and peak value. According to the conclusion that the bulges are in the middlefrequency band

researches on the first four order frequency show that the gas bulge is related to the back attack.