The present application discloses an LED light string control system, which comprises a direct-current power supply, a polarity change control unit and a forward-reverse connection LED light string circuit, wherein the direct-current power supply is electrically connected with the polarity change control unit, and the polarity change control unit is electrically connected with the forward-reverse connection LED light string circuit. The present application further discloses an LED light string control method, which comprises: a polarity change control unit outputs a changed-polarity voltage with a specific frequency according to a timing sequence; and LED lamps with the corresponding polarity in a forward-reverse connection LED light string circuit are lighted according to the polarity-changed voltage.