Tidal flats, which represent a wide landsea interaction zone, are difficult to measure. The lack of historical topographic data has seriously affected the development and utilization of tidal flats. Using a tidal flat of radial sand ridges as an example, waterlines under different tide conditions were extracted from TM and MSS remote sensing images from around 1987, and sea surface heights were simulated with a Mike21 hydrodynamic model. Elevations were assigned to the waterlines. The digital elevation model was obtained through the terrain iteration process. The results show that, in the tidal flat of radial sand ridges, there is a strong correlation between the topographic results obtained from the waterline method and the measured data from the nautical chart, with a coefficient of determination (R2) of 0.864, a mean absolute error of 0.37m, and a root mean square error of 0.41m, indicating that the topographic results can be further used to analyze the morphologic evolution of the tidal flats.