A bottom drying type sludge drying device comprising: a housing provided with a partition having a curved face for separating a space in the housing into at least one first drying chamber and at least one second drying chamber, wherein the first drying chamber is arranged above the second drying chamber; a feed gate for the sludge to be dried and an outlet for the drying gas that has dried the sludge provided in an upper portion of the at least one first drying chamber, respectively, and a discharge gate for the dried sludge provided in the circumferential wall of the at least one first drying chamber; at least one inlet for the drying gas for the sludge to be dried provided in a side wall or bottom of the at least one second drying chamber; the partition having at least one depressed area, wherein the depressed area has the shape of an arc, at least one communication opening is shaped at the depressed area, and a bridge-shaped element is positioned above the at least one communication opening, whereby at least one lateral aperture is defined between the bridge-shaped element and the partition, wherein a longitudinal direction of the at least one communication opening intersects with or is perpendicular to a longitudinal direction of the housing, wherein the bridge-shaped element strides over the communication opening along the longitudinal direction of the communication opening and is substantially parallel to said longitudinal direction of the communication opening, wherein the bridge-shaped element has a greater length than the communication opening, so that the bridge-shaped element stride across the communication opening in the longitudinal direction of the communication opening like a bridge and wherein the two ends of the bridge-shaped element are fixed on the partition adjacent to the end edge of the communication opening respectively, and wherein there is a curved path from the at least one communication opening to the at least one lateral aperture such that the drying gas enters from the at least one second drying chamber into the at least one first drying chamber; and at least one sludge stirring assembly (7a, 7b) provided in the at least one first drying chamber, having a rotary shaft (701a, 701b) and at least one stirring unit (702a, 702b) fixed on the rotary shaft (701a, 701b), wherein the at least one stirring unit (702a, 702b) is configured to cut, break and stir the sludge and configured so that a front end thereof faces and is close to the at least one lateral aperture, such that the front end scrapes the sludge in or at the at least one communication opening as the at least one stirring unit (702a, 702b) rotates. a housing provided with a partition having a curved face for separating a space in the housing into at least one first drying chamber and at least one second drying chamber, wherein the first drying chamber is arranged above the second drying chamber; a feed gate for the sludge to be dried and an outlet for the drying gas that has dried the sludge provided in an upper portion of the at least one first drying chamber, respectively, and a discharge gate for the dried sludge provided in the circumferential wall of the at least one first drying chamber; at least one inlet for the drying gas for the sludge to be dried provided in a side wall or bottom of the at least one second drying chamber; the partition having at least one depressed area, wherein the depressed area has the shape of an arc, at least one communication opening is shaped at the depressed area, and a bridge-shaped element is positioned above the at least one communication opening, whereby at least one lateral aperture is defined between the bridge-shaped element and the partition, wherein a longitudinal direction of the at least one communication opening intersects with or is perpendicular to a longitudinal direction of the housing, wherein the bridge-shaped element strides over the communication opening along the longitudinal direction of the communication opening and is substantially parallel to said longitudinal direction of the communication opening, wherein the bridge-shaped element has a greater length than the communication opening, so that the bridge-shaped element stride across the communication opening in the longitudinal direction of the communication opening like a bridge and wherein the two ends of the bridge-shaped element are fixed on the partition adjacent to the end edge of the communication opening respectively, and wherein there is a curved path from the at least one communication opening to the at least one lateral aperture such that the drying gas enters from the at least one second drying chamber into the at least one first drying chamber; and at least one sludge stirring assembly (7a, 7b) provided in the at least one first drying chamber, having a rotary shaft (701a, 701b) and at least one stirring unit (702a, 702b) fixed on the rotary shaft (701a, 701b), wherein the at least one stirring unit (702a, 702b) is configured to cut, break and stir the sludge and configured so that a front end thereof faces and is close to the at least one lateral aperture, such that the front end scrapes the sludge in or at the at least one communication opening as the at least one stirring unit (702a, 702b) rotates.