An exhaust gas purifying and heat recovering system for sludge treatment, comprising: a first heat exchange flow path including a first heat exchanger, and a second heat exchanger and a third heat exchanger arranged downstream of the first heat exchanger, a first heat exchange medium is circulated in the first heat exchange flow path, to heat process gas in the first heat exchanger, the process gas is directed to a sludge treatment device disposed downstream of the first heat exchanger; a second purification and heat exchange flow path including a heat exchange tank containing a second liquid heat exchange medium, the exhaust gas after sludge treatment is discharged into the heat exchange tank, is purged by the second liquid heat exchange medium in the heat exchange tank, and transfers the heat to the second liquid heat exchange medium so as to be cooled, the second heat exchanger is disposed in the heat exchange tank to transfer heat of the second liquid heat exchange medium to the first heat exchange medium in the second heat exchanger; a fourth purified gas recovery flow path, the exhaust gas of the heat exchange tank flows through the third heat exchanger to exchange heat with the first heat exchange medium flowing through the third heat exchanger, and flows through the fourth purified gas recovery flow path, at least a portion of the exhaust gas after being heat exchanged is directed back to the first heat exchanger via an intake port to recycle the process gas; a third dirty liquid separation flow path including a dirty liquid separation tank provided between a dirty liquid outlet of the heat exchange tank and a clean liquid inlet of the heat exchange tank, for separating the dirty liquid after purging the exhaust gas, and the separated liquid is again directed to the clean liquid inlet of the heat exchange tank; and a gas distribution device disposed upstream of an intake conduit of the heat exchange tank for receiving the exhaust gas from the sludge treatment device and enabling the sludge-treated exhaust gas to evenly enter the heat exchange tank, the intake conduit being disposed below the level of the second liquid heat exchange medium in the heat exchange tank, and the intake line is inserted at a depth sufficient to ensure sufficient heat exchange between gas and liquid. a first heat exchange flow path including a first heat exchanger, and a second heat exchanger and a third heat exchanger arranged downstream of the first heat exchanger, a first heat exchange medium is circulated in the first heat exchange flow path, to heat process gas in the first heat exchanger, the process gas is directed to a sludge treatment device disposed downstream of the first heat exchanger; a second purification and heat exchange flow path including a heat exchange tank containing a second liquid heat exchange medium, the exhaust gas after sludge treatment is discharged into the heat exchange tank, is purged by the second liquid heat exchange medium in the heat exchange tank, and transfers the heat to the second liquid heat exchange medium so as to be cooled, the second heat exchanger is disposed in the heat exchange tank to transfer heat of the second liquid heat exchange medium to the first heat exchange medium in the second heat exchanger; a fourth purified gas recovery flow path, the exhaust gas of the heat exchange tank flows through the third heat exchanger to exchange heat with the first heat exchange medium flowing through the third heat exchanger, and flows through the fourth purified gas recovery flow path, at least a portion of the exhaust gas after being heat exchanged is directed back to the first heat exchanger via an intake port to recycle the process gas; a third dirty liquid separation flow path including a dirty liquid separation tank provided between a dirty liquid outlet of the heat exchange tank and a clean liquid inlet of the heat exchange tank, for separating the dirty liquid after purging the exhaust gas, and the separated liquid is again directed to the clean liquid inlet of the heat exchange tank; and a gas distribution device disposed upstream of an intake conduit of the heat exchange tank for receiving the exhaust gas from the sludge treatment device and enabling the sludge-treated exhaust gas to evenly enter the heat exchange tank, the intake conduit being disposed below the level of the second liquid heat exchange medium in the heat exchange tank, and the intake line is inserted at a depth sufficient to ensure sufficient heat exchange between gas and liquid.