In order to investigate one kind of new underwater acoustical passive jamming materials,the underwater burning of pyrotechnic composition having pulsating combustion effect was studied. The acoustic frequency characteristic formatted from the underwater burning of pyrotechnic composition was also studied with the testing system for underwater acoustic. The reasons for its formation were discussed. Results show that 15 g pyrotechnic composition having pulsating combustion effect can form the sound pressure as high as 340 Pa. Its corresponding acoustic pressure level is 51 dB. The time of burning can last 18.5 s.The acoustic frequency is mainly between 0-2000 Hz in the band of lowfrequency.