Structural　robustness　reflects　the　insensitivity　of　a　structure　system　to　local　damages.　To　evaluate　the　progressive　collapse　resistance　of　steel　frames,　a　quantitative　assessment　method　for　the　robustness　of　steel　frames　is　presented.　By　considering　the　contributions　of　structural　members　to　the　structural　energy　distribution　and　the　influence　areas　of　localized　damage　of　structural　members,　a　method　for　calculating　the　importance　indices　of　members　is　given,　which　can　be　used　to　determine　the　most　possibly　unfavorable　initial　damage　modes　of　a　frame　structure.　By　analyzing　the　steel　member　load　capacity　redundancy　and　the　strain　energy　sensitivities　of　individual　members,　a　structural　redundancy　index　of　steel　frames　is　brought　forward　based　on　the　localized　damage　modes,　which　is　directly　proportional　to　the　member　load　capacity　redundancy　and　inversely　proportional　to　the　member　strain　energy　sensitivity.　The　minimum　of　the　structural　redundancy　indices　is　employed　to　measure　the　robust　performance　of　a　steel　frame,　after　discussing　the　differences　in　definition　between　structural　redundancy　and　structural　robustness.　A　quantitative　assessment　approach　to　structural　robustness　of　steel　frames　in　terms　of　damage　mode　based　structural　redundancy　is　proposed,　and　the　scope　of　its　application　is　then　analyzed.　Finally,　an　example　of　8-story　space　steel　frame　is　given　to　demonstrate　the　feasibility　of　the　presented　approach　to　evaluating　the　structural　robustness　of　steel　frames.