Abstract: In order to study the fine structure of air-to-water sound transmission in shallow water, State Key Laboratory of Acoustics, Institute of Acoustics conducted an experiment in the South China Sea in March, 2013. During the experiment, multi-frequency signals transmitted by a hooter were received by an underwater hydrophone, and the distance between the hooter and the hydrophone was from 2.4 km to 9.8 km approximately. Through analyzing experimental data in this work, the experimental air-to-water transmission loss at frequencies 128 Hz and 256 Hz is estimated with the range up to 9.8 km, which has clear oscillation structure. The wave-number integration approach is used to simulate theoretical air-to-water transmission losses and to explain the experimental air-to-water sound transmission characteristic.