In　recent　years,　China　has　experienced　significant　economic　growth　and　some　degree　of　environmental　pollution　control.　However,　achieving　a　perfect　balance　between　the　environment　and　economic　development　remains　a　challenge.　In　order　to　seek　solutions　to　this　issue　and　promote　the　sustainable　development　of　cities,　this　paper　starts　from　the　urban　level,　which　is　relatively　lacking　in　existing　research.　Based　on　the　panel　data　of　urban　indicators　from　2013　to　2021,　it　quantifies　the　environmental　performance　of　key　cities　using　the　slack-based　measure　(SBM)　model　of　super-efficiency　based　on　a　non-expected　output.　Furthermore,　it　utilizes　the　Tobit　panel　regression　model　suitable　for　limited　dependent　variables　to　analyze　the　impact　of　driving　factors　on　the　environmental　performance　of　key　cities,　and　it　further　explores　the　reasons　for　the　loss　of　urban　environmental　performance　from　the　dual　perspectives　of　inputs　and　outputs.　The　research　findings　indicate　the　following.　(1)　The　average　environmental　performance　of　30　key　cities　has　shown　an　increasing　trend　but　has　not　yet　reached　a　valid　state.　The　cities＇　environmental　performance　rises　in　the　range　of　[0.444,　0.821],　indicating　that　there　is　room　for　improvement　in　urban　environmental　management.　(2)　Cities　in　the　northeastern　region　of　China　have　lagged　behind　the　eastern,　central,　and　western　regions　in　terms　of　environmental　performance　over　this　nine-year　period,　and　the　redundancy　of　undesirable　outputs　is　partly　responsible　for　this　decline.　(3)　The　large　proportion　of　the　secondary　industry,　the　number　of　vehicles　on　the　road,　and　the　population　density　have　a　significantly　negative　impact　on　urban　environmental　performance,　while　the　per　capita　regional　GDP　and　urban　maintenance　and　construction　funds　make　a　positive　difference.　These　research　findings　provide　a　scientific　basis　and　valuable　insights　into　urban　environment　performance　enhancement　and　can　serve　as　a　reference　for　areas　in　need　of　balanced　development　between　the　urban　environment　and　economic　growth.