The invention discloses a low-voltage compensation device and method of an energy-saving power distribution network. The device is divided into a rectification part, an inversion part and a bypass unit, wherein the rectification part comprises a relay QF1, a filtering capacitor C1, an AC reactor L1, an IGBT tube G1, a rectification diode and a photovoltaic cell panel, the inversion part comprisesa relay QF2, an IGBT tube G2, an IGBT tube G3, an inversion inductor L2 and a filtering capacitor C2, and the bypass unit comprises a bidirectional thyristor SCR. With the adoption of a series voltagecompensation mode, the problem of low voltage of the power distribution network is solved, and the device only needs to provide a part of load power; with the adoption of a transformerless DC seriesmode, the problems of loss and non-linearity of the transformer are prevented; combined with photovoltaic power generation, a working mode is switched, and the problem of extremely low voltage of a plurality of voltage regulation devices simultaneously running at access points is solved; and meanwhile, photovoltaic power generation is fully utilized, the effect of energy saving and emission reduction is achieved.