The invention discloses a sludge pretreatment device which comprises a support plate, a support, a discharge nozzle, a loading bin, a motor, an impeller, a keep-off nozzle, a lower grid, guide rods, an upper grid, a swinging mechanism, a connecting plate, a spacing plate and a steel ball. The swinging mechanism further comprises a bracket, a power mechanism, rotating shafts, cams, sliding plates, guide wheels and a reset mechanism; the reset mechanism further comprises a push top, a spacing rod, and a spring. The sludge pretreatment device is simple in structure, sludge is continuously pressed into the upper grid through the impeller, the swinging mechanism pushes the upper grid to move reciprocatingly, the sludge is crushed horizontally and longitudinally under the common action of the upper grid and the lower grid, the sludge can be sliced evenly, continuously and rapidly, the sludge is allowed to fall into the discharge nozzle rapidly through continuous conveying of the impeller, and high efficiency is achieved.