In　this　study,　a　continuous　fiber　laser　(1064　nm　wavelength,　30　W/cm(2))　is　used　to　irradiate　multi-walled　carbon　nanotubes　(MWCNTs)　on　different　substrate　surfaces.　Effects　of　substrates　on　nano-welding　of　MWCNTs　are　investigated　by　scanning　electron　microscope　(SEM).　For　MWCNTs　on　silica,　after　3　s　irradiation,　nanoscale　welding　with　good　quality　can　be　achieved　due　to　breaking　C-C　bonds　and　formation　of　new　graphene　layers.　While　welding　junctions　can　be　formed　until　10　s　for　the　MWCNTs　on　silicon,　the　difference　of　irradiation　time　to　achieve　welding　is　attributed　to　the　difference　of　thermal　conductivity　for　silica　and　silicon.　As　the　irradiation　time　is　prolonged　up　to　12.5　s,　most　of　the　MWCNTs　are　welded　to　a　silicon　substrate,　which　leads　to　their　frameworks　of　tube　walls　on　the　silicon　surface.　This　is　because　the　accumulation　of　absorbed　energy　makes　the　temperature　rise.　Then　chemical　reactions　among　silicon,　carbon　and　nitrogen　occur.　New　chemical　bonds　of　Si-N　and　Si-C　achieve　the　welding　between　the　MWCNTs　and　silicon.　Vibration　modes　of　Si3N4　appear　at　peaks　of　363　cm(-1)　and　663　cm(-1).　There　are　vibration　modes　of　SiC　at　peaks　of　618　cm(-1),　779　cm(-1)　and　973　cm(-1).　The　experimental　observation　proves　chemical　reactions　and　the　formation　of　Si3N4　and　SiC　by　laser　irradiation.