The　key　issue　of　the　progressive　collapse　(PC)　design　of　RC　frame　structures　at　large　deformation　stage　is　to　calculate　the　PC　resistance　demand　of　the　structure　under　catenary　mechanism.　The　existing　design　codes　for　PC　design　are　unsafe　because　of　ignoring　the　effect　of　nonlinear　dynamic　behavior　of　PC　resistance　demand　under　catenary　mechanism.　According　to　the　theoretical　framework　of　the　PC　resistance　demand　analysis　based　on　the　energy　conservation　principle,　the　relationship　between　the　nonlinear　dynamic　and　nonlinear　static　PC　resistance　demands　for　RC　frame　structures　under　catenary　mechanism　was　derived.　And　the　theoretical　method　to　calculate　the　PC　resistance　demand　of　RC　frame　structures　under　catenary　mechanism　was　established.　At　last,　the　proposed　method　describing　the　PC　resistance　demand　relationship　of　RC　frames　with　catenary　mechanism　was　validated　through　numerical　examples.