A simplified model of corona discharge on overhead wire has been proposed for propagating surge computations using the finite-difference time-domain method. The radial progression of corona streamers from the wire is represented as the radial expansion of cylindrical conducting region whose conductivity is several tens of microsiemens per meter. Two wire radii are considered: 5 and 2 mm, in order to simulate two experimental configurations by Noda. The critical electric field on the surface of a 5-mm radius wire for corona initiation is set to E-0 = 1.8 or 2.9 MV/m. For a 2-mm radius wire, it is set to E-0 = 2.2 MV/m. The critical background electric field necessary for streamer propagation is set to E-cp = 0.5 MV/m for positive voltage application, and E-cn = 1.5 MV/m for negative voltage application. The computed waveform of radial current (including both conduction and displacement currents) agrees well with the corresponding measured waveform. Also, the computed relation between the total charge (charge residing on the wire and emanated corona charge) and applied voltage (qV curve) agrees well with the corresponding measured one, except for relatively low applied voltages. Additionally, the increase of coupling between the energized wire and another one nearby due to corona discharge is well reproduced.