W18O49 nanowires exhibit stable field emission at low fields. To explore the potential application of such nanowires in backlight and display devices, it is necessary to achieve uniform emission on a large area. In the present study, the authors demonstrate that field-emission uniformity of large-area samples may be improved by following an electrical-current treatment procedure. This is due to the increase in the number of nanowires that join in the field emission during the process, in which a small number of strong emitters are gradually melted down. The process of self-melting occurring in field emission is studied using a point anode in situ with a scanning electron microscope. The self-melting is attributed to the effect of Joule heating occurring due to passing of current through field electron emitting nanowires. These results are useful for the device application of W18O49 nanowires as large-area cold cathodes.