Internal solitary waves (ISWs) are studied west of Dongsha islands in the northern South China Sea (SCS) using acoustic backscatter data in August 2021. Simultaneous satellite images and XBT profiles are incorporated to understand their propagation and evolution processes at depths 110-180 m. A comparison of acoustic backscatter images and simultaneous XBT profiles revealed that acoustic imaging provided fine water structures with a small difference above 150 m. Three soliton trains (ISW1, ISW2, and ISW3) with apparent vertical and horizontal scales of –20∼30 and -160~380 m, respectively, are captured by the acoustic section. Their propagation speeds are 1.0m·s-1 and 1.2m·s-1 and 1.5m·s-1, respectively. The observed characteristics of ISW are more consistent with those by using theoretical two-layer Korteweg-de Vries (KdV) models. ISW1 exhibits complex waveform characteristics, while ISW3 has an asymmetric waveform structure influenced by the slop topography. suggesting that strong dissipation of these two ISWs. Joint observations from high-resolution acoustic and hydrographic techniques provide a comprehensive approach to overcoming the limitations of single instrument measurements, and enhance our understanding of the complex propagation processes of ISWs in the northern SCS.