The invention relates to a sludge drying device. The sludge drying device comprises a feeding hopper, a feeding screw rod group, a tank body, a discharging hole and the like, wherein the feeding hopper is fixed on the tank body, the discharging hole is formed in the tank body, the feeding screw rod group is located at the bottom of the feeding hopper and is used for assisting feeding; a steam jacket, steam inlets and condensed water outlets are formed in the periphery of the tank body, and the steam jacket forms a steam channel; a drying cavity is formed in the tank body and is communicated with the feeding hopper and the discharging hole, and a sufficient space is formed in the drying cavity for dispersing moisture produced during the hydration of the sludge; and a pushing screw rod groupis located in the drying cavity, is of a hollow structure and forms another steam channel. According to the sludge drying device, partial dried sludge is returned to the feeding hole during the feeding and is premixed with to-be-treated wet sludge, so that the total water content of the fed sludge is controlled to be 40% or below 40%, and the sticking problem of the sludge is avoided; and the water content of the discharged sludge treated by the sludge drying device can be generally decreased to about 5%, so that the volume of the sludge is greatly reduced, the purposes of water reduction, volume reduction and harmlessness are achieved, and the sludge can be conveniently stored and transported.