The main body of the dewatering machine is composed of the fixed ring and the swimming ring, and the spiral axis penetrates into the filter device. The first part is the concentrated part, the latter part is the dehydration department. The filter joint formed between the fixed ring and the swimming ring and the pitch of the helical shaft gradually become smaller from the thickening part to the dewatering part. Spiral shaft rotation in the promotion of sludge from the concentration of the department to the dehydration department, but also continue to drive the swimming ring cleaning filter, prevent blockage. Sludge concentrated in the concentration of the Ministry of gravity after being transported to the dehydration department, in the process of advancing with the filter and pitch gradually smaller, as well as back plate blocking action, resulting in a great internal pressure, shrinking volume, to achieve full dehydration.