Manual processing of underwater digital elevation model (DEM) consumes more time and brings efficiency-bottleneck problems.An automatic underwater DEM processing system for the Yangtze River,which is composed of the automatic water depth data monitoring and reading module,automatic DEM processing module,automatic thematic map processing module and process monitoring and displaying module is proposed.The input water depth data could be processed into regular grid DEMs and thematic maps automatically and efficiently by the system.The system can reduce human workload and achieve real-time DEM data processing,and solve the aforementioned efficiency-bottleneck problems.