Carbon nanotubes (CNTs) with diameters of 10 or 100 nm have been screen printed on indium tin oxide/glass substrates and treated by an adhesive tape or a KrF excimer laser. After the surface treatment, the field emission characteristics of CNT cathodes have been measured. The lower turn-on electric fields have been obtained for the CNT cathodes with a CNT diameter of 10 nm. Then a high electric field pulse aging has been performed to get more uniform emission images. Finally, the field emission lifetimes of CNT cathodes have been measured. The lifetimes of the CNT cathodes treated by tape peeling have been only several hours at a dc measurement, whereas the lifetimes of the CNT cathodes treated by a KrF excimer laser, regardless of the CNT diameter, reached 100 h, corresponding to 100 000 h at a duty ratio of 1/1000.