The　structures　or　structural　members　made　of　high-strength　steel　may　have　time-varying　mechanical　properties　in　whole　life-cycle　due　to　the　ageing　effects.　In　particular,　the　corroded　steel　structures　in　high-seismicity　regions　could　have　unexpected　failure　modes　when　subjected　multi-directional　excitations.　Therefore,　in　this　study,　the　mechanical　properties　of　Q690　steel　H-section　columns　during　the　life-cycle　under　bi-directional　cyclic　loads　are　investigated.　Firstly,　a　refined　finite　element　(FE)　model　is　built,　which　takes　the　time-varying　of　corrosion　characteristics　into　consideration.　Then,　the　degradations　of　mechanical　property　and　failure　mechanisms　of　steel　columns　with　different　design　parameters　at　whole　life-cycle　are　analysed　by　the　FE　models.　Finally,　a　quantitative　calculation　method　of　ultimate　resistance　and　damage　index　of　steel　columns　considering　ageing　effects　is　proposed.　The　findings　demonstrate　that　several　factors　affect　the　ultimate　strength　of　steel　columns　during　the　life-cycle　stage,　with　the　axial　compression　ratio　and　flange　width-thickness　ratio　having　the　greatest　impacts　on　the　ultimate　capacity.　The　ageing　effect　decreases　the　plastic　flow　capacity　of　steel　columns,　increases　the　stress　concentration,　and　induces　the　failure　mode　transition　from　plastic　flow　to　buckling　failure.　The　ageing　effect　may　be　accurately　estimated　by　the　suggested　calculation　method　for　the　ultimate　capacity　and　damage　index　of　steel　columns　at　the　life-cycle　stage.　The　findings　of　this　study　highlight　the　significance　of　taking　into　account　the　ageing　effects　of　steel　columns　in　the　seismic　design.