A novel method based on the arc characteristic for single-phase self-adaptive reclosuer on ultra high voltage transmission line is presented in this paper. Building up secondary arc model through the MODELS modular of EMTP-ATP，this paper simulates that the secondary arc repeatedly burn and extinguish when transient fault occurs. It extracts the busbar transient voltage signal using the multi-resolution morphological gradient of the mathematic morphological , the differential spectrum energy of voltage can be used to determine whether the fault is permanent or transient.EMTP simulation data shows that this method can identify the fault narture and correctly implement the self-adaptive reclosure.