The internal solitary waves are studied by analysis of optical remote sensing images in the whole sea area of the Northern South China Sea. This paper mainly collects MODIS optical remote-sensing images from Jan.2015 to Dec.2018, and the amplitude inversion model of internal solitary waves applicable to deep sea and shallow sea in the Northern South China Sea are established by using neural network. The calculation results of the model are compared with the situ data in the Northern South China Sea, and the accuracy is higher than 15% for both shallow sea and deep sea. Using the inversion model, the amplitude distribution of internal solitary waves in the Northern South China Sea is obtained. It is found that the amplitude distribution is positively correlated with water depth, with a correlation coefficient of 0.81. The amplitude distribution of internal solitary waves in Wenchang sea area, Dongsha atoll area and deep sea basin was calculated. It is found that the amplitude of single internal solitary waves is different. The amplitude of internal solitary waves in Wenchang sea area, Dongsha atoll area and deep sea basin is positively correlated with the water depth, with correlation coefficients of 0.79, 0.91 and 0.81 respectively. This study provides a new method for inversion of internal solitary waves amplitude in both deep and shallow areas of Northern South China Sea.