Abstract: To study the mechanism of the earthquake production, we need to study the propagation characteristics of the groundsill extreme-low frequency(ELF) electromagnetic wave. The electromagnetic fields excited by the groundsill ELF arbitrary linear antenna may be the sum of the electromagnetic fields excited by the ELF dot sources. The expressions of electromagnetic fields excited by the groundsill ELF linear antenna in earth-ionosphere cavity are derived from the expressions of the electromagnetic fields excited by the ELF dot sources. The field intensity spatial distribution maps of the electromagnetic fields excited by the ELF single linear antenna and two linear antennas are obtained by the speed numerical convergence algorithm. The strong and weak field intensity values in the spatial distribution are expressed by the color code. The field intensity values of the horizontal electric field component are less than those of the vertical component, whereas, the field intensity values of the horizontal magnetic field component are larger than those of the vertical component. Furthermore, the field intensity values excited by two linear antennas are larger than those excited by the single linear antenna.