A carbon fiber for a field electron emitter has a coaxial stacking morphology of truncated conical tubular graphene layers, each of which includes a hexagonal carbon layer and has a large ring end and a small ring end at opposite ends in the axial direction. The edges of the hexagonal carbon layers are exposed on at least part of the large ring ends. Since all the exposed edges function as electron emission tips, a large amount of emission current can be obtained.