The invention belongs to the technical field of steelmaking and discloses a method for reducing the total slag amount of a full-tri-de technology for a converter. The method includes the following steps that in the full-tri-de technology, slag in a decarbonizing furnace finishing tapping is sent into a dephosphorizing furnace; a slag thickening agent is added into the dephosphorizing furnace for the slag thickening operation, and thickening of liquid slag is accelerated; scrap steel is added into the dephosphorizing furnace, molten iron is added, and smelting is conducted; after the dephosphorizing furnace completes smelting, molten steel is poured out and sent into the decarbonizing furnace, and smelting is conducted; and the above steps are repeated in the full-tri-de technology, and final slag of the decarbonizing furnace is continuously recycled. The technical effects that the utilization rate of smelting consumables is increased, the smelting efficiency is improved, and the total slag amount is reduced are achieved.