Abstract: The tree-contact incipient fault, often regarded as a disturbance, is frequently ignored. However, its intermittent and frequent occurrence can cause serious accidents such as disconnection of lines and fire. By studying its generation mechanism and development process, and extracting fault signal characteristics, the detection and identification of tree-contact incipient fault can be realized, thus the operation and maintenance level of distribution lines can be improved. Based on magneto-hydrodynamic simulation and fault tests, the development process and fault waveform characteristics of the arc in separation phase are studied. The results show that, as the branch is gradually separated from the wire, the length of the arc increases and the temperature of the arc decreases, leading to an increase in the duration of the zero current time of the fault current waveform. The temperature of the arc is higher when the aluminum stranded wire acts as the anode, meanwhile, when the current is reversed from positive to negative, the duration of the zero current time is significantly longer than that when the current is reversed from negative to positive. The occurrence of the aforementioned characteristics is due to the generation and development mechanism of the failure, and it is not affected by the speed of branch movement and the type of tree. The results can lay a foundation for further realization of the tree-contact incipient fault.