The invention particularly relates to a buoy capable of changing the detecting depth. The buoy comprises a buoy main body, a control system and a lifting device. The lifting device comprises a transmission, a sensor and a second winder. The control system is connected with the sensor and the transmission, and the transmission is connected with the second winder. The sensor is located at a second opening formed in the bottom of the buoy main body. The transmission is controlled through the control system to enable the second winder to rotate, then the sensor is driven to rise and fall to changethe detecting depth, the sensor can be lowered below the sea surface through the second opening to conduct detecting, the detecting range is wide, and the flexibility is good.