A down conductor cathode protection and corrosion prevention method comprises the following steps that the soil of a buried part of a down conductor (1) is excavated out to the position about 20 cm underground; outer paint, higher than the position 5 cm below the horizon line, of the down conductor is removed and cleaned up, the paint removing portion is polished bright through abrasive paper, and the paint removal length is greater than 5 cm; a sacrificial anode (2) and a connection clamp (3) are fixed to the paint removal portion of the down conductor through bolts (4), and good contact is ensured; the sacrificial anode is fixed to the connection clamp through one bolt, and it is ensured that contact is good and the sacrificial anode extends deeply into the ground by at least 20 cm in the direction of the down conductor; soil (5) is backfilled to the original height and trodden down, and the sacrificial anode forms cathode protection for the down conductor. By means of the method, the sacrificial anode forms cathode protection and corrosion prevention for the easily-corroded buried portion of the down conductor specifically, and the method has the characteristics that construction is convenient, materials are easy to obtain and the corrosion prevention effect is good.