The development of waterway transportation and the increase of bridge lead to more and more ship-bridge collision accidents. In view of the limitation of vessel traffic service and passive system for bridge piers against ship collision in inland waterway, an active early-warning system for bridge piers against ship collision was proposed. There are certain complementary in target detection with infrared camera and target detection with visual camera. We have designed an active early-warning system for bridge piers against ship collision, which is based on target detection with the infrared/visual camera and laser. The system, which can warn the ships that will strike the bridge piers with acousto-optic stably and reliably under all-weather, all-day, full automatic condition will decrease ship-bridge collision accidents and protect the bridge and ship.