Abstract: The water distribution device with vaulted baffle-perforated plates and strainers always introduces bias flow in high-flowrate mixed bed (HFMB) polisher. This paper analyzes the issue and figures out the root cause as the deform and damage of the perforated plates. Then the design scheme of water distribution device with vaulted baffle–double perforated plates is proposed, in which the design parameters are optimized through computer simulation technology of fluid mechanics. The new scheme has been applied in technical renovation engineering project of water distribution device in HFMB polisher of a 680 MW ultra-supercritical unit. The result after three months of operation shows that by applying this water distribution device with double perforated plates there were very little differential pressure during operation while the water distribution is uniform with stable water quality in HFMB polisher. The volume of periodic water production has increased from 66,000 m³ to 109,000 m³, which is of great significance for water saving and emission reduction.