One-dimensional nanomaterial possesses an electric field reinforcing effect, and its field emission properties have aroused much interest. In this paper, ZnO nanowire (NW) arrays are prepared by the thermal chemical vapor deposition (CVD) method, and the characteristic of field electron emission of ZnO NW arrays under the illumination of ultraviolet light is investigated. It is found that, upon ultraviolet light illumination, the turn-on voltage drops off and emission current increases. A process of field emission coupled with semiconducting properties of ZnO NWs is proposed. Ultraviolet photon-excited electron transition from valence band to conductance band and defect energy levels of ZnO NWs can lead the number of emitting electrons to increase, and the photoemission reduces the effective work function of zinc oxide emitters, which largely enhances the field emission performance. The characteristic of field emission of ZnO NWs under ultraviolet light illumination suggests an approach to tuning field emission of semiconductor emitters, which is promising for the applications in optical sensor, cold-cathode flat panel display and field electron source.