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Exposed to thundercloud and downward leader, coupling with operation voltage, glow corona discharge could be ignited in the vicinity of the UHVDC transmission line, leading to space charge layer, which could influence subsequent upward leader process from ground wires and conductors. To investigate the effect of space charge on lightning shielding performance of UHVDC transmission line, based on charge simulation method and upstream element method, the numerical calculation model of space charge distribution of ±1100kV UHVDC transmission line under thundercloud and downward leader was established in this paper, combined with leader inception and propagation model. The space distribution of space charge was obtained and the effect of space charge on exposure arcs of ground wires was analyzed. Meanwhile, the effect of corona space charge on upward leader parameters of ground wires and conductors, such as leader length, leader current, and leader velocity, were discussed quantitatively and qualitatively. Results showed that space charge inhibited leader inception and propagation, and had a more inhibitory effect on ground wires. Therefore, considering space charge, the upward leader was more likely to generate from the conductors and finish the final jump process. Further investigations on the inhibitory effect of space charge were carried out using space potential distortion. Results in this paper could provide data support for lightning shielding analysis of the UHVDC transmission line.