The invention discloses a method and device for desulfurizing flue gas of a thermal power unit burning high sulfur coal. The device comprises a burnt lime bin 1, a burnt lime slaker 2, a cyclone reactor 3, a wet desulphurization tower 4, a wet-type electrostatic precipitator 5 and a chimney 6, wherein the bottom of the burnt lime bin 1 is connected with the cyclone reactor 3 through the burnt lime slaker 2; the bottom of the cyclone reactor 3 is provided with an oxidation pond 7, and the top of the cyclone reactor 3 is connected with the wet desulphurization tower 4 through a connecting pipeline; the wet-type electrostatic precipitator 5 is arranged at the top of the wet desulphurization tower 4; and the exhaust port of the wet-type electrostatic precipitator 5 is connected with the chimney 6. According to the invention, the flue gas emitted by the thermal power unit burning the high sulfur coal is ensured to meet the national emission standard after treatment; and moreover, the powerconsumption and the equipment initial investment are effectively reduced, the floor area of the equipment is reduced, and the utilization ratio of the system is improved.