Remotely operated underwater vehicle (ROV) is employed in the nondestructive inspection of erosion damage of a deep-buried long tunnel after long-term operation to offer data basis for safety evaluation and maintenance. The defectives and deposits on concrete surface, the abrasion of tailrace floor, and the integrity of contact locations are inspected via full-coverage scanning using sonar in the ROV system; important parts and sonar-inspected abnormal areas are verified through videos obtained by autonomous underwater vehicle. This engineering practice provides engineers with the operation status of deep-buried long tunnel subjected to long-term scouring. In addition, the advantages and shortcomings of the application of ROV are also presented.