Background　Previous　studies　have　shown　that　both　age　and　hemoglobin　are　closely　associated　with　the　prognosis　of　septic　shock.　A　recent　study　found　that　hemoglobin　may　change　with　age.　Hemoglobin-to-Age　Ratio　(HAR)　takes　both　age　and　hemoglobin　into　consideration　as　essential　factors.　So　far,　the　effect　of　HAR　on　the　prognosis　of　septic　shock　is　still　unclear.　This　research　aimed　to　investigate　the　association　between　the　HAR　and　the　prognosis　of　patients　with　septic　shock.Methods　Cox　proportional　hazards　regression　analysis,　restricted　cubic　spline,　Kaplan-Meier　survivor　analysis　and　stratified　interaction　analysis　were　used　to　elucidate　the　relationship　between　the　HAR　and　prognosis　of　patients　with　septic　shock.Results　There　is　a　nonlinear　association　between　the　HAR　and　mortality　within　28　days　after　intensive　care　unit　admission.　When　the　HAR　was　lower　than　0.13,　mortality　within　28　days　after　ICU　admission　decreased　significantly　as　the　HAR　increased.　When　the　HAR　was　higher　than　0.13,　the　HAR　was　not　a　protective　factor　for　mortality　within　28　days　after　ICU　admission.　In　patients　with　septic　shock,　the　HAR　was　more　effective　in　reducing　the　risk　of　death　in　patients　with　atrial　fibrillation　than　in　patients　without　atrial　fibrillation.Conclusion　There　is　a　nonlinear　association　between　the　HAR　and　mortality　within　28　days　after　intensive　care　unit　admission.　When　the　HAR　was　at　a　low　level,　mortality　within　28　days　after　ICU　admission　decreased　significantly　as　the　HAR　increased.　When　the　HAR　was　at　high　levels,　the　HAR　might　not　be　a　protective　factor　for　mortality　within　28　days　after　ICU　admission.　In　patients　with　septic　shock,　the　HAR　was　more　effective　in　reducing　the　risk　of　death　in　patients　with　atrial　fibrillation　than　in　patients　without　atrial　fibrillation.