Abstract: Underwater engineering surveying is usually to use single-beam echo sounders and a little attention is paid to the engineering after completion. A multi-beam echo sounder is used to survey the engineering of precast concrete slabs connected with hinges to protect the Yangtze River embankment of Nanjing river stretch which has been built for four years. Through the contrast of the terrain of cross-sections among a recent observation and before construction and after construction, the form of cross-sections and the engineering area are stable, the design indexes reach the desired effects.