The invention relates to a power system automation technology, in particular to a novel flexible multi-state switch device and a control method thereof. The novel flexible multi-state switch device comprises a multi-feeder distribution network and loads. The novel flexible multi-state switch device further comprises a converter, multiple bidirectional thyristors and loads. The converter comprisesan energy storage device, an IGBT module and an LCL filter. The energy storage device and the IGBT module are connected in parallel with each other, and are incorporated to the multi-feeder distribution network after being connected in series with the LCL filter. Each bidirectional thyristor is connected in series between each feeder and the corresponding load. The novel flexible multi-state switch device is connected with the multiple feeders in the power grid. When the voltage of the power grid is normal, the device is used for making compensation for the harmonic and reactive power in the loads. When voltage sag occurs in the power grid, the device quickly cuts off the power supply to a feeder with voltage sag and transfers the loads to a feeder in normal operation. With the device adopted, the loads can be smoothly transferred when voltage sag occurs in the power grid, and continuous and high-quality power supply to important loads can be realized.