The invention provides an underwater oil spillage tracking and detecting buoy system capable of tracking and warning semi-submersible oil. The underwater oil spillage tracking and detecting buoy system comprises a diving part and a non-diving part. The diving part comprises a buoy terminal and an underwater extension device. The non-diving part comprises a monitoring platform and an external data chain. The external data chain forms a wireless transmission linking channel between the buoy terminal of the diving part and the monitoring platform of the non-diving part through a satellite and a base station. After being thrown in a water area polluted by spilled oil, the diving part together with the semi-submersible oil drifts along with water flow close to the surface layer, and acquires detection information of the spilled oil in water, then, the detection information of the spilled oil in the water is transmitted to a detection circuit module through an oil spillage sensor and transmitted to the monitoring platform through a communication module with the help of a communication satellite net and a ground base station, therefore, the state parameters of all working modules are acquired and controlled, and remote monitoring on the buoy terminal and underwater semi-submersible oil tracking and detecting information is realized. The underwater oil spillage tracking and detecting buoy system capable of tracking and warning the semi-submersible oil can monitor the displacement and diffusion conditions of the underwater semi-submersible oil in real time, and is novel in conception and convenient to operate, thereby providing an important technological means for an emergency rescue department.