Through　analyzing　the　impact　of　the　factors　of　catalyst　deactivation,　different　factors　are　classified　according　to　timeliness　characteristics.　In　this　research,　experiments　were　made　under　the　condition　of　coal　combustion　flue　gas　on　a　coal-fired　boiler　to　study　the　characteristics　of　the　early　deactivation　of　the　SCR　catalyst.　Analysis　shows　that　the　main　cause　of　early　deactivation　of　catalyst　is　chemical　poisoning　(mainly　alkali　metal)　and　pores　clogging　on　the　surface　of　the　catalyst.　While　the　main　cause　of　long-term　deactivation　is　deeper　chemical　poisoning,　pores　clogging　and　the　chemical　form　changes　of　elements　on　the　surface　of　the　catalyst.　Through　analyzing　the　influence　of　the　factors　of　catalyst　deactivation,　separate　factors　are　classified　according　to　timeliness　characteristics.　This　research　provides　a　strong　fundamental　support　to　clear　the　deactivation　mechanism　of　the　SCR　catalyst.　©　2018　American　Society　of　Mechanical　Engineers.　All　rights　reserved.