Abstract: Introduction The structural design of desulfurization anti-corrosion flue gas duct in wet FGD is always a difficult point. Method Technical code for design of thermal power plant air & flue gas ducts/raw coal & pulverized coal piping(DL/T 5121-2000) and the auxiliary calculation method,which is used to guide the design of thermal power plant air & flue gas ducts, make no distinction between desulfurization anti-corrosion flue gas duct and usual flue gas duct design, and for larger stiffener, combined stiffener cross section parameters of (8~［22a) and (I10~I28a) were only listed in the code, it limited the usage specifications of stiffener. Result Combining the engineering fact, this paper revises the rigidity calculation formula of stiffener space according to the plate allow deformation of desulfurization anti-corrosion flue gas duct. Conclusion The design detail of cross & triangle inner brace is proposed to reduce the difficulty of anti-corrosive construction. This paper also gives a simple method to expand combined stiffener cross section parameter, thus to provide some reference for the design of desulfurization anti-corrosion flue gas duct.