Optical Remote Sensing offers an alternative to traditional hydrographic surveys for measuring water depth, with the advantage of low cost and large area. The multi-spectral image of SPOT-5 with the high resolution provides possibility for bathymetric mapping. In order to estimate the image's potential for the retrieval of water depth, we use single-band model and dual-band model separately to inverse the water depth with worked example from Naozhou Island in Guangdong, China. The actual depth is derived from the chart to establish inversion models and to assess the accuracy of inversed water depth based on the criterions of the mean relative error and the mean square error. The result illustrates that the dual-band model is superior to the single-band model and the red-band model is superior to the green-band model. Compared with the other segments of water depth, the mean relative errors in shallow water between 0m and 5m are the biggest, which make the overall errors of all models big. However, the dual-band model is relatively better than the single-band model in shallow water, its mean relative error is about 22%, and its mean square error is about 1.87m. We have a conclusion that the multi-spectral image of SPOT-5 has a good ability to inverse water depth, and its high resolution can describe more detail topographic information under water. Bathymetry by Remote Sensing becomes an important assistant means for traditional bathymetry methods.