The invention discloses a low voltage regulation system and a control method and a control device thereof. The low voltage regulation system comprises a series transformer, a parallel transformer, a selector switch, and a control circuit. The primary side of the series transformer is connected in series to the load side of a power supply line. The primary side of the parallel transformer is connected in parallel to the load side of the power supply line, and the secondary side of the parallel transformer is provided with multiple branch connectors. The input end of the selector switch is connected with the secondary side of the parallel transformer, and is connected with the multiple branch connectors at the secondary side of the parallel transformer. The selector switch is used for selecting a branch connector connected to a loop. The output end of the selector switch is connected with the secondary side of the series transformer. The control circuit is connected with the selector switch, and is used for making the selector switch select a branch connector to be connected so as to regulate the compensation voltage. By controlling the branch connectors at the secondary side of the parallel transformer, the voltage can be adjusted to different values, namely, the ratio of transformation can be changed. When the voltage of a power supply line of a grid drops, compensation is made for the voltage of the line. Therefore, the qualified rate of supply voltage and the quality of electric energy are improved, the needs of users are satisfied, and the governance efficiency of low voltage is improved.