Abstract: In order to study the effect of corona space charge on the initiation of subsequent streamer discharges of the UHVDC overhead transmission line during thunderstorms, a 2 D numerical simulation model is established to calculate the distribution of the corona space charge during a thunderstorm based on a second-order accurate finite volume method and Kaptzov’s assumption. The accuracy of the model was verified by comparing the measured and simulated corona discharge current of horizontal single line under dynamic electric field. The corona current waveform and space charge distribution characteristics of a typical ±1100 kV UHVDC overhead transmission line subjected to the thundercloud and the downward leader was calculated. It is concluded that the descending process of downward leader will significantly increase the density of positive ions in vicinity of ground wires, where the distance to the ground wire is in the range of about 0.5 m. The maximum value of corona discharge current of the conductor and the ground wire increases 6～7 orders of magnitude in response to the downward leader, when compared with the steady state value under the thundercloud electric field. As the increasing of the positive ion density near the surface of the ground wire, the location of the maximum electric field will moves far away from the surface of the ground wire. It will trigger the initiation of the subsequent streamer discharge. The work lays a foundation for further study on the influence of the space charge layer on the lightning attachment to UHVDC overhead transmission line.