A thermionic electron emission device includes an insulating substrate and one or more lattices located on the insulating substrate. Each lattice includes a first, second, third and fourth electrode down-leads located on the insulating substrate to define an area. A thermionic electron emission unit is located in the area. The thermionic electron emission unit includes a first electrode, a second electrode, and a thermionic electron emitter. The thermionic electron emitter includes a carbon nanotube film structure. The carbon nanotube film structure includes a carbon nanotube film. The carbon nanotube film includes a number of carbon nanotubes joined end to end along axial directions of the carbon nanotubes by contacting with each other directly.