Knowing bottom geoacoustic parameters is of great importance for using sonar systems effectively in shallow water. This study is based upon the vertical line array (VLA) in South China Sea experiment of the Asian Seas International Acoustic Experiment (ASIAEX), dated from May 3, 2001 to May 16, 2001, in which the ambient noise was also measured in shallow water. Beamforming is used to calculate the vertical directionality of ambient noise, but limited by the array element spacing, the major analysis frequency range is 100 to 400 Hz. Comparison between forward modeling (normal mode code) and experimental results show the energy ratio of up-looking and down-looking beams, which can be referred to the energy reflection coefficient of the bottom-potentially a function of angle and frequency. From the reflection coefficient, critical parameters of the sediments such as sound speed, density, and attenuation coefficient can be obtained. Finally, this result is verified by on-site chirp sonar surveys during the experiment, and also by other inversion investigation in this area using other sound source.