Abstract: The acoustic propagation characteristics in a canyon environment were analyzed using the data from the northern South China Sea.The experimental and numerical results show that the energy begins to bend to a deeper place with the depth change of the trench and the sound Transmission Losses (TLs) reach the maximum near the center of the trench due to the combined effect of the negative gradient sound velocity profile and the seabed topography.As the sea goes shallower gradually,the energy is concentrated due to the seafloor reflection,thus the TLs reduces by over 20 dB compared with the TLs results in the simple slope to the deep sea environment.What's more,when the convergence effect is less than the combination of the loss caused by diffusion and seafloor reflection,TLs are minimized and then increase with range.In the last segment,the gradual convergence of the energy is again highlighted,and the TLs decrease 10 dB when the sea depth suddenly changes from 850 m to 311 m in 8 km.Finally,the ray theory and the parabolic equation methods are used to explain the convergence effect of sound field in a canyon environment.