Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes and cubic and spherical carbon nanocages, have been prepared by an ethanol thermal reduction process. Scanning electron microscopy studies showed that carbon nanotubes predominated. Transmission electron microscopy investigations indicated that as-synthesized sample contained mostly bamboo-shaped carbon nanotubes, with some carbon cubic and spherical nanocages. Detailed examination of high-resolution transmission electron micrography showed that the walls of bamboo-shaped carbon nanotubes consisted of oblique graphene planes with respect to the tube axis, whose interlayer spacing was about 0.335 nm. The experimental results suggest that the growth mechanism of the bamboo-shaped carbon nanotubes follows the base growth model and the appearance of cubic and spherical carbon nanocages arises from the graphitic sheets bending in an attempt to eliminate the highly energetic dangling bonds present at the edge of the growing structure. At the same time, we report that the correlative reaction factors influence the morphology of carbon nanomaterials and elucidate the formation mechanism of different carbon structures.