Addressing the bottlenecks of low efficiency and insufficient accuracy stability in traditional tide gauge measurements,and the insufficient for power and endurance of unmanned survey vessel (USV) during inland channel dredging projects in Sichuan Province caused by complex hydrological conditions such as swift currents and fluctuating water levels,we systematically investigate a non-tide-gauge underwater topographic surveying method and its precision control techniques.The method integrates mobile vessel-mounted RTK (real-time kinematic) with echo sounders,using the lower reaches of the Minjiang River as a representative case study.By establishing a collaborative platform integrating the RTK real-time positioning system with digital echo sounders,and applying key technologies such as real-time sound velocity correction,precise control of instrument verticality,optimisation of multi-region coordinate transformation parameters for survey areas,and dynamic regulation of vessel speed and attitude,we thoroughly identify critical error sources affecting measurement accuracy under complex hydrological conditions,and propose a multi-dimensional accuracy control strategy.The findings demonstrate that the non-tidal gauge survey mode exhibits significant technical advantages and engineering applicability in rapid-flow and non-steady-flow bathymetric scenarios.It provides high-precision,high-efficiency surveying technical support for the similar conditions,while also offers crucial practical reference for the development and application of intelligent USV.