The influence of the secondary arc on the power system is more and more serious with the rise of voltage levels. If the secondary arc can not be extinguished promptly, the single-phase auto-reclosing will fail. In order to reduce the secondary arc extinction time, there by ensuring the success of the single-phase auto-reclosing, Jindongnan-Nanyang-Jingmen UHV AC demonstration project is used as an example. This paper analyses the factors affecting the secondary arc current using PSCAD/EMTDC. The simulation results are coincident with the theoretical analysis. The conclusions drawn from this paper will be excellent references to the future UHV (ultra high voltage) projects.