Based on Fluent, the flow distribution in flue gas cooler and its inlet and outlet flue in a power plant was numerically simulated. The calculation results show that the flue gas velocity distribution at the import of flue gas cooler was imbalance. The no uniform distribution of flue gas velocity can easily lead to problems such as wear, ash deposition and uneven heat transfer. To address the problem of uneven distribution of flue gas velocity, a diversion structure is designed and installed in the inlet flue of flue gas cooler. The numerical calculation results show that compared with the original flow distribution structure, the diversion structure can make the flow distribution of the flue gas cooler and its inlet and outlet flue more uniform, which can effectively avoid the problems of wear, ash deposition and uneven heat transfer.