The invention provides a combined device capable of self-purifying discs and strengthening sludge dewatering by utilizing latent heat. The combined device is characterized in that a spiral sludge conveyor is arranged at the bottom of an inclined tube sedimentation tank; an inclined tube is laid above the spiral sludge conveyor; the lower part of the inclined tube sedimentation tank is connected with a wet carbonation reactor via a hydraulic pump; a nano aeration disc is arranged at the bottom of the wet carbonation reactor; the sludge in the wet carbonation reactor is guided into a moist heat drying device; motors are installed at one end of the moist heat drying device and drive two driving shafts horizontally arranged in parallel to rotate; the driving shafts are in a hollow structure; an air inlet is formed at one end of each driving shaft and a drain hole is formed at the other end of the driving shaft; two spiral turntables arranged in parallel are arranged on the driving shafts horizontally; the surfaces of discs on the sections, close to a support, of the spiral turntables are smooth and the surfaces of the discs on the rest sections are bestrewed with small holes. The invention also discloses a method for drying the sludge by utilizing the device.