Forthesynthesisofsingle-walledcarbonnanotubes(SWCNTs)fromCH4overaFe/MgOcatalyst,weproposedacoupledDowner-turbulentfluidized-bed(TFB)reactortoenhancetheselectivityandyield(orproductionrate)ofSWCNTs.Bycontrollingaveryshortcatalystresidencetime(1-3s)intheDowner,onlypartofFeoxidescanbereducedtoformFenanoparticles(NPs)availableforthegrowthofSWCNTs.ThepercentageofunreducedFeoxidesincreasedandtheyieldofSWCNTsdecreasedaccordinglywiththeincreaseofcatalystfeedingrateinDowner.SWCNTswerepreferentiallygrownonthecatalystsurfaceandinhibitedthesinteringoftheFecrystalliteswhichwouldbeformedthereafterinthedownstreamTFB,evidencedbyTEM,RamanandTGA.ThecoupledDowner-turbulentfluidized-bedreactortechnologyallowedhigherselectivityandhigherproductionrateofSWCNTsascomparedtoTFBalone.