The invention discloses a detection system for underwater corrosion. The detection system comprises an operation mother ship. The operation mother ship is connected with an underwater robot through asteel cable. A mechanical arm is arranged at the underwater robot. A visual unit is arranged at the position, close to the front end, of the mechanical arm. A corrosion probe is arranged at the frontend of the mechanical arm. The operation mother ship and the underwater robot are further provided with wire cables. The system adopts the underwater robot with a crawler walking mechanism, the visualunit and the corrosion probe are arranged on the mechanical arm of the underwater robot and used for collecting all data of the surface corrosion degree of an underwater structure, the corrosion probe adopts an electromagnet to achieve the adhesion function, a stable working environment is provided for detection, and the system is wholly reasonable in design, high in working stability coefficientand high in adaptability, and has good practicality.