Abstract: To study the characteristics of corona onset voltage of double-circuit UHVDC overhead transmission lines, a computation model is established in this paper based on the gas discharge theory and with consideration of the power line's arrangement and the stranded conductor's actual structure. According to the different mechanism of positive and negative corona onset, the corona onset voltages of each pole's sub-conductor are calculated on the basis of solving the surface space electric field of stranded conductor by using the optimized charge simulation method. The impacts of the line arrangement, air temperature, air pressure and parameters of stranded conductors on corona onset voltage are analyzed and discussed. The results show that the value of corona onset voltage is much higher for the -+/-+ line arrangement. In addition, the increase of conductor radius, air pressure and bundle number can significantly raise the corona onset voltage. The height of line to ground, anode-cathode distance, the height difference between upper line to lower line and the bundle spacing can also affect the corona onset voltages to varying degrees. When the stranding ratio of the stranded conductor is close to zero, the corresponding corona onset voltage will also be close to the one of the smooth conductor.