Abstract: The present invention provides a ballast water treatment system, comprising a centrifugal separator, an ultrasonic sterilizer, and an ultraviolet sterilizer, wherein, the centrifugal separator is designed to separate large-particle of foreign matters from the ballast water by centrifugal separation by means of density difference; the ultrasonic sterilizer is arranged at the back of the centrifugal separator, and is designed to accomplish ultrasonic sterilization for the ballast water passing through the centrifugal separator; the ultrasonic sterilizer comprises a pipe that is used for sterilization of the ballast water and ultrasonic irradiation unit that perform ultrasonic irradiation for the ballast water passing through the pipe; the ultraviolet sterilizer accomplishes sterilization by means of ultraviolet irradiation for the ballast water passing through the ultrasonic sterilizer.