Abstract: Conducting bathymetric surveys in steep and deep waters of high dams and large reservoirs, such as the Three Gorges and the lower reaches of Jinsha River, conventional single-beam echo sounders are affected by vessel attitude, time-delay effects, and beam angle effects, leading to deteriorated underwater depth measurement accuracy.To enhance bathymetric accuracy in the steep and deep waters of high dams and large reservoirs, a design scheme for single-beam measurement equipment integrated with an inertial navigation system (INS) is proposed.By embedding attitude sensors and applying ultra-wideband (UWB) transducers, the system integrates the attitude sensor with the single-beam transducer into a unified device.This innovation addresses attitude compensation and time synchronization issues while effectively mitigating the impact of beam angle effects to a significant extent.Field testing of the bathymetric equipment was conducted in steep and deep waters near the dam areas of the Three Gorges and Wudongde reservoirs.Results demonstrate that the measurements exhibit strong consistency across multiple survey voyages on different cross-sections, with high internal consistency accuracy.Fixed-point tests performed at two benchmark sites reveal a relative deviation of 0.01% in water depth measurements and mean elevation errors of 0.11 m and 0.07 m, respectively.The research outcomes comply with the permissible error requirements for bathymetric measurements specified in the Chinese Industry Standard SL 257—2017 Specifications for Waterway Survey.This equipment effectively meets the requirements for hydrological and sediment monitoring in steep and deep waters of high dams and large reservoirs, significantly advancing the technical capabilities for such monitoring tasks.