This article is concerned with the calculation of the corona current-voltage characteristics of a unipolar high-voltage direct current (HVDC) transmission line with a single conductor stretched above the ground plane. In light of justified assumptions, the corona charge density around the conductor surface is obtained using an iterative procedure. This makes it possible to calculate the corona current for a given applied voltage. It is interesting to note that the per-unit charge density around the conductor surface with reference to its value at the gap axis has the same distribution irrespective of the conductor radius and height above the ground plane as well as of the applied voltage. Along this axis, Deutsch's assumption is waived and the charge density is calculated as being dependent on the conductor radius, conductor height, onset voltage, and applied voltage. A curve-fitting polynomial is made for the per-unit distribution of charge density around the conductor surface. Determination of the surface charge density at the gap axis and the polynomial describing the per-unit charge density distribution represent the basis of a proposed simplified method for quick calculation of the I-V characteristics, irrespective of the conductor radius and height above the ground plane. The corona current-voltage characteristics, as calculated by the proposed simplified approach, are compared with those calculated before and with those measured in different laboratories. The computation time is drastically reduced when using the proposed simplified method.