The invention discloses an automatic power transmission device, structurally comprising a bottom plate, a grounding ball, a connecting sleeve and fixing bolts, wherein the bottom plate has a square structure, fixing bolts are movably installed on four corners of the bottom plate, the grounding ball is arranged at the middle of the surface of the bottom plate, the connecting sleeve is installed atthe middle of the top of the grounding ball, an earth lead electrically connected with a tower pole is connected with the grounding ball after passing through the connecting sleeve, the grounding ballis buried in the soil, and the grounding ball is composed of an insertion rod, a wring port, a hemispherical shell, an installation tin seat, a lead and a hollow cavity. According to the automatic power transmission device disclosed by the invention, the contact area between the grounding ball and the soil is increased mainly by the cooperation of the grounding ball, the connecting sleeve and thelike, thereby ensuring full contact between the grounding ball and the soil and protecting the installation tin seat, the electric conduction is not affected even if the soil is frozen, a pressure can also be applied to a cylinder to deform the cylinder, the connection position between the connecting sleeve and the grounding ball is also easy to be loosened, thereby being convenient to maintain,and meanwhile the sharp corner of a V-shaped iron wire and the grounding wire rub against each other to remove the ice covering the surface.