For　economic　activities,　energy　is　a　necessary　component　of　production.　As　the　world＇s　largest　energy　consumer　and　carbon　emitter,　China　faces　greater　resource　constraints　and　environmental　pressure　in　the　background　of　global　climate　change,　improving　energy　efficiency　is　the　inevitable　path　for　long-term　development.　However,　the　energy　efficiency　in　China　at　this　stage　is　relatively　low,　thus　improving　energy　efficiency　is　urgent.　Based　on　the　panel　data　from　the　database　of　Chinese　industrial　enterprises　and　the　database　of　Chinese　industrial　enterprises＇　pollutant　emissions　between　2003　and　2012,　this　paper　empirically　conducts　a　thorough　investigation　on　the　nonlinear　impact　of　spatial　agglomeration　and　enterprises＇　energy　efficiency,　and　further　examine　its　heterogeneity　and　mechanisms.　The　results　show　that:　(1)　There　is　a　significant　U-shaped　link　between　spatial　agglomeration　and　enterprises＇　energy　efficiency.　(2)　Based　on　agglomeration　externalities,　scale　effect,　learning　effect,　competition　effect,　and　policy　effect　are　the　internal　mechanisms　through　which　spatial　agglomeration　impacts　on　enterprises＇　energy　efficiency.　(3)　The　effects　of　spatial　agglomeration　on　enterprises＇　energy　efficiency　are　influenced　by　technology　level,　energy　consumption　level,　agglomeration　patterns,　and　enterprise　characteristics.　Based　on　the　empirical　findings,　we　suggest　that　enterprises　take　full　advantage　of　the　benefits　brought　by　spatial　agglomeration,　and　that　the　government　encourage　the　growth　period　of　spatial　agglomeration　to　become　more　profound,　more　synergetic,　and　more　diverse.