The invention relates to a steel-making electric furnace structure and a late campaign lance descending method thereof. With increasing of the furnace age of an electric furnace, a refractory material in the furnace is corroded, a combustion chamber is enlarged, the problem that the late campaign liquid steel level is lowered is unavoidable even though raw material molten iron and steel scrap charging amount is increased, after the liquid steel level is lowered, the distance between an oxygen lance and the liquid steel level is increased, the oxygen utilization rate is reduced, and consequently, the problems that smelting consumption is increased and the smelting period is prolonged occur. A late campaign lance descending solution is designed, magnesia carbon bricks are placed between the positions, where oxygen lances are located, of water-cooling frames and bottom water-cooling boards, and the magnesia carbon bricks are removed when a second tap hole of the electric furnace is substituted so that the oxygen lances can be lowered. In terms of actual conditions of electric furnace smelting, after lance descending, the electric furnace smelting consumption is substantially reduced, consumption of oxygen and natural gas of steel per ton is reduced, and meanwhile, the smelting period is shortened remarkably.