According to the parameter and boundary conditions of the 1000 kV UHV AC power transmission demonstration project provided by State Grid Corporation of China , this paper uses transmission line distributed parameter method, computes theoretically the current harmonic of charging current turn-on, fault in different locating in Southeastern in Shanxi Province via Nanyang in Henan Province to Jingmen in Hubei Province of the 1000 kV UHV AC power transmission demonstration project. This result shows that those phenomena occurred in demonstration project short circuit transition processing, and the effect on relay protection. It is useful for relay protection in the 1000 kV UHV AC power transmission demonstration project.