Abstract: In order to analyze the characteristics of the acoustic radiation and phenomenon of the pyrotechnic composition combustion underwater,the high speed photography has been used to study the behavior of the bubble at exit, which was generated by the pyrotechnic composition combustion underwater.The bubbles' volume were estimated with high speed film sequences,and their change acceleration were obtained by getting second-order derivative through the fitting curve of the bubble-volume,then the sound pressure of the noise were calculated based on the equation of point sound source of pulsation volume.Results show that the bubbles were mainly flattened sphere,because of the effects of the Bjerknes and buoyancy force on the interface,when the pyrotechnic composition is combusting underwater,the sound pressure of the noise from the exit is up to 177.1 Pa.