The invention discloses a sulfur dioxide cooling device for an afterheat boiler in the technical field of boiler afterheat treatment. The device comprises a cylinder; the upper and lower ends of the cylinder communicate with an upper smoke box and a lower smoke box; an air inlet is formed in the side wall of the upper smoke box; an air outlet is formed in the side wall of the lower smoke box; three sets of water change ports are formed in the outer wall of the cylinder; and heat exchange tubes are uniformly mounted in an inner cavity of the cylinder. The device is simple in structure and reasonable in design; cooling water is injected in the cylinder through the water change ports; high-temperature sulfur dioxide gas is quickly cooled when passing through the inner cavity of the cylinder;the cooling water absorbs heat to become hot water; through utilization of the afterheat, the energy consumption is reduced; and meanwhile, the sulfur dioxide gas can be quickly cooled to meet the production and use requirements.