Selective　catalytic　reduction　(SCR)　De-NOx　is　a　high-efficient　flue　gas　denitration　technology;　its　efficiency　is　impacted　by　many　factors　and　flow　field　distribution　uniformity　lists　in　the　most　important　technical　indicators,　while　which　weighs　flow　field　distribution　uniformity　significantly　is　the　maximum　coefficient　of　variation　(CV)　of　the　flue　gas　velocity　at　the　evaluation　sectional　surface.　SCR　reactor＇s　inlet　section　was　redesigned　in　order　to　tackle　the　issue　that　the　CV　value　at　the　evaluation　sectional　surface　far　exceeded　the　standard　evaluation　limit　for　the　SCR　reactor　with　sudden　expansion　inlet.　The　updated　arrangement　was　simply　structured　and　easily　fabricated　with　the　uniform　flow　field　distribution　which　was　simulated　and　verified　by　an　advanced　CFD　software　Star-ccm+.　The　numerical　simulation　indicated　that　the　velocity　uniformity　at　the　inlet　section　was　improved　greatly　and　the　maximum　CV　value　was　below　the　standard　limit.　Constructive　reference　would　be　drawn　from　the　update　in　terms　of　the　study　on　the　internal　structure　of　SCR　reactor.