Abstract: The transmissionline theory is used to calculate the latetime HEMP induced sheath current of long lines with different length and termination, which is located near or above the ground. The results show that the induced sheath current on the line with two grounded ends can reach to tens of As. As the line's length grows, the peak value of the sheath current increases, and the increase with the length slows down. When one end of a line have high serial resistance in the grounded wire(the other end is grounded), the peak value of the sheath current decreases obviously.