When the machine starts running, the sludge is pushed into the filter cartridge from the feed inlet and then moves to the sludge cake outlet under the pushing of the helical axis blades. Because the gaps among the helical axis blades will gradually getnarrower, the sludge is under heavier pressure. Then the water gradually comes out from it according to the pressure differential and the filtering space between the fixed plates and the moving plates. Relying on the self-cleaning function of the fixed plates and the moving plates, block can be well avoided. At last, the sludge cakes are pushed by helical axis after being fully dewatered and then discharge for the outlet.