The invention discloses a total recycling system for diffused fuel gas in a material tank at the top of a blast furnace and a safe overhauling method for the total recycling system. Three diffusion pipes are respectively arranged at the highest point of elevation, the front part of an ejection valve group and a second dust remover of the total recycling system for the diffused fuel gas in the material tank, and nitrogen sweeping points are arranged in front of a cut-off valve of the second dust remover and an access valve group of a fuel gas pipe network. By virtue of the cooperation of the diffusion pipes and a nitrogen sweeping manner, the fuel gas is replaced with nitrogen in the diffused fuel gas recycling system, and CO content of gas in the diffused fuel gas recycling system is decreased to a safe value, so that the safety of a maintenance worker is not threatened. By virtue of the cooperation of the diffusion pipes and the nitrogen sweeping manner, air is replaced with nitrogenin the diffused fuel gas recycling system before the diffused fuel gas recycling system is recovered to be used, and the O2 content of gas in the diffused fuel gas recycling system is decreased to a safe value, so that the explosion caused by the mixing of the diffused fuel gas in the pipe network and oxygen is avoided, and the safe overhauling is achieved.