Pyramid sharp pyrolysis flame is a new method for carbon nanotubes synthesis. Oxy-acetylene flame outside the frustum of pyramid sharp reactor provides the necessary high temperature circumstance for carbon nanotubes synthesis, while inside the interior mixture of CO, H2, He, and iron pentacarbonyl (Fe(CO)5) is heated. CO is used as the source of carbon, Fe(CO)5 as the source of catalyst precursor. Special structure of the frustum of pyramid sharp reactor makes the oxy-acetylene flame folded gradually above the reactor. And it meets the condition that the interior mixture which has reacted initially under high temperature and will flow out of reactor avoids exposing to air completely and burning abundantly. Immersing a sampling substrate into the incomplete burning flame can gain carbon nanotubes. By adjusting the distance between the oxy-acetylene flame jet and the synthesis area, achieved the purpose that just changing one factor of synthesis or pyrolysis temperature while the other one constant, then respectively studied the effects of them on experimental. The perfect synthesis temperature in experimental is about 595°C, while the pyrolysis temperature is about 1000°C.