In this paper, the monopolar corona equation is solved using a modified finite element method (FEM) to give the corona current caused by overhea dc transmission lines without using the commonly-used Deutsch's assumption The method is free from empiricism and entails implicitly a decrease of thsurface field intensity of the conductor with the applied voltage in the same manner as observed experimentally. This in itself represents an additional improvement for the analysis of ionized field where the approximation pertinent to the assumption of constant surface field intensity is mitigated. The calculated corona current as well as the current density at the ground plane agreed with those measured experimentally for a laboratory model