Pyramid shaped pyrolysis flame is a new method for carbon nanofibes (CNFs) synthesis. Oxy-acetylene flame outside the frustum of pyramid shaped reactor provides the necessary high temperature environment, while CO is used as the source of carbon, iron pentacarbonyl (Fe(CO)5) as the source of catalyst precursor in reactor. Inside, the mixture of CO, H2, and Fe(CO)5 will burn incompletely after initial reaction under high temperature. Inserting a sampling substrate into the incomplete burning flame can gain CNFs. Field emission scanning electron microscope (FE-SEM) was used to illustrate the results of experimental. By adjusting the distance between the oxy-acetylene flame jet and the synthesis zone, studied the effects of pyrolysis and synthesis temperature. The preferable pyrolysis temperature in experimental is about 693°C while the synthesis temperature is about 595°C, and preferable synthesis temperature is about 535°C while pyrolysis temperature is about 1000°C. It can be also concluded that when the synthesis temperature is high (595°C, comparing with 535°C), preferable pyrolysis temperature is low (693°C, comparing with 1000°C), vice versa. Effects of sampling substrate were also studied. Using 304 stainless steel wire as sampling substrate can not gain CNFs, while 201 stainless steel plate can gain straight and uniform, and silicon chip can gain curly ones.