Under　service　loading　and　environmental　actions,　the　corrosion　of　steel　strands　would　reduce　the　cracking　load　and　ultimate　load　of　post-tensioned　concrete　(PTC)　beams.　It　also　leads　to　the　degradation　of　flexural　stiffness,　and　hence　increases　the　deflection　of　beams　under　the　same　load.　In　order　to　more　effectively　evaluate　the　stiffness　degradation　of　corroded　post-tensioned　concrete　(CPTC)　beams,　an　empirical　model　is　proposed　in　this　work　for　assessing　the　stiffness　considering　the　effect　of　the　corrosion　of　steel　strands.　In　the　proposed　model,　cracking　stiffness　and　stiffness　after　cracking　are　assessed　separately,　and　the　equations　of　cracking　moment　and　ultimate　moment　are　derived.　The　proposed　model　is　verified　by　experimental　data.　Results　show　that　the　proposed　model　can　efficiently　predict　the　stiffness　changes　during　the　whole　loading　process,　and　the　deflections　predicted　by　the　proposed　model　are　in　good　agreement　with　experimental　values.　The　proposed　model　is　proved　to　be　able　to　efficiently　predict　the　stiffness　degradation　of　CPTC　beams　caused　by　corrosion　of　steel　strands,　and　can　reveal　the　dependence　of　flexural　stiffness　on　the　corrosion　loss　of　steel　strands　and　the　external　loads.　©　2023　Elsevier　Ltd