Abstract: As the sole solid material in the lower part of a blast furnace (BF), the multiphase reaction behavior of coke within the deadman region of the hearth is of significant theoretical and practical importance for carbon emission control and low-carbon production. The multidimensional characterization of the occurrence state, multiphase reaction behavior, and renewal mechanism of deadman coke in the hearth was performed through the dissection of a 3200-m³ BF, combining various methods such as rope-sawing residual iron removal, image processing techniques, microscopic analysis, and coke dissolution experiments. The results showed that the deadman root in the hearth exhibited a “curved” shape and a distinct “floating” state, with the floating height at the center approximately 0.45 m, increasing toward the hearth edge. Vertically, the deadman was divided into three regions: the “slag–coke zone,” the “iron–coke zone,” and the “coke–free zone.” The average deadman voidage was calculated to be 54.75% (±0.85%), and the coke particle size was (21.47 ± 0.53) mm (±0.53 mm), based on image processing techniques. A “slag + CaS isolation layer” was identified on the outer surface of the deadman coke during the dissolution and erosion process of hot metal analysis of the “slag–iron–coke” three-phase microstructure indicated that this layer suppressed the carburization reaction and represented the most limiting factor for deadman coke renewal. A coke renewal formula was established from the coke dissolution experiments, and the renewal time was calculated to be 14.74 d. The renewal mechanism of deadman coke was elucidated through comprehensive analysis, and recommendations for low-carbon operation were proposed. These findings provide a scientific basis and theoretical guidance for low-carbon production and fuel optimization in ironmaking blast furnaces.