Abstract: The combustion of pyrotechnic composition underwater has ability to form a low-frequency underwater sound signal. The French defense company of Lacroix pyrotechnic Group developed a "pyrotechnic-acoustic transmitter" in 1995. However, until now this investigation has not been extensively studied and reported. In this paper, the research of mechanism of the acoustic radiation for pyrotechnic composition combustion underwater was conducted. The results show that the emission noise mainly includes turbulence noise and breakdown bubble noise. The further investigation also revealed that the breakdown bubble noise has the dominant effect comparing with the turbulent noise. In order to prove this viewpoint, the underwater combustion of pyrotechnic composition with pulsating combustion effect was studied through a deep experimental investigation.