Firstly, each-part of the unmanned detection system underwater and their function characteristics were discussed in detail. And then this system was used in reserved rock bar blasting underwater exploration of some project. Corresponding investigation scheme was designed, which included conducting the camera shooting by ROV(remotely operated vehicle) and underwater positioning by acoustic positioning system. Moreover, this ROV did not only take the photograph underwater on broken rock blocks, but also could look for unblasting rock mass. The ROV position and forward direction were determined by the acoustic positioning system. And the shape, height, slope and profile of a muckpile were determined by ROV forward path. Finally, the effect of rock bar blasting was comprehensive evaluated.