Direct　coupling　of　alkanes　via　C-H　activation　of　terminal　methyl　groups　has　acquired　tremendous　interests　both　scientifically　and　technically.　Herein　we　present　the　results　of　linear　alkane-coupling　at　the　step　edges　of　Cu　surfaces　at　modulated　temperatures.　Combining　the　observations　of　scanning　tunneling　microscopy　(STM)　with　density　functional　theory　plus　dispersion　(DFT-D)　calculations,　we　elucidate　the　mechanism　of　the　reaction　and　demonstrate　that　the　low　activation　barrier　relies　on　heterogeneous　catalysis　at　the　upper　step　edges,　where　low-coordinated　surface　atoms　are　present.　We　further　reveal　the　generality　of　the　reaction,　so　that　it　can　be　applied　on　the　step　edges　of　different　facets　of　surfaces.