In order to solve the problem of internal slurry circulation and water balance of the double-tower double-cycle wet-FGD system in the limestone-gypsum desulfurization process, a simple slurry circulation mode between the two towers was proposed and applied in a flue gas desulfurization system of a 2×350 MW unit in Shanxi. The results showed that the design desulfurization efficiencies of the first-stage tower and the second-stage tower were 87% and 97%, respectively. The design was simplified while the replacement of spare parts was improved. The slurry circulation between two towers was established by liquid level difference design and forced circulation pump. The slurry of the first-stage tower was diverted to the second-stage tower through the slurry circulation system, and the excess slurryof the second-stage tower overflowed back to the first-stage tower to build a water balance system between the two towers. Under the working conditions of 187 MW or 290 MW, 4-layer spraying could reach 99.81% desulfurization efficiency after the slurry circulation system was started. Compared with independent operation mode of two towers in the double towers system, the new double - tower circulation mode could guarantee the desulfurization efficiency by starting 6 circulating pumps, and reduce the system resistance by about 500 Pa and the fan power consumption by 400 kW.