The precast concrete slab connected with hinges is a new structure of embankment protection, and has been successfully applied to some embankment protection projects. However, since the size of underwater slab is very small, the underwater layout of concrete slab is difficulty to be detected, which brings about difficulty to the appraisal of underwater construction quality. Through analyzing and comparing various underwater inspection techniques, we present the multi-beam echo sounding with ultra high resolution which is applied to the investigation of embankment protection with hinge-connected concrete slabs in Wuhan segment of Yangtze River. This technique is proved to be advantageous in the inspection of underwater precast concrete slabs connected with hinges, and could also be applied to similar underwater engineering.