The invention relates to a seawater detection system, comprising a device box, a base and a detection cage which are sequentially fixed from top to bottom; a communication mechanism, a locating mechanism, a controller and a storage battery are fixedly arranged in the device box; the base is of a cone-shaped structure with big top and small bottom; a plurality of fixed seats are fixed at the lowerend of the base, a detection plate is fixed at the lower end of each fixed seat, and sensors used for detecting water quality are respectively fixed at the two sides of each detection plate; the detection cage is of a cylinder structure with the upper end open; each detection plate is arranged in the detection cage; a plurality of upright posts are fixed outside the detection cage, the upper end of each upright post is fixed with the lower end of the base, and the lower end of each upright post is fixed with a pedestal of the detection cage; a plurality of baffles are fixed from top to bottomon two adjacent upright posts, and each baffle is tilted downwards in arrangement from the inside of the detection cage towards the outside of the detection cage; and the controller is respectively connected with the communication mechanism, the locating mechanism, the storage battery, the detection plates and the sensors by virtue of an electrical signal.