There are hydraulic press and mechanical press types of alternating press dewaterer. This machine adopts hydraulic press. The hydraulic pressure is provided by the hydraulic station and up and down traveling of the hydrocylinder is controlled by the hand-directional valve. The water is pressed out by a huge external force formed during the down traveling of the hydrocylinder, thus realizing dewatering. And in course of the up traveling of the hydrocylinder, the material is pushed out of the feed box and discharged out manually, while the other feed box is pushed into the hydrocylinder, the alternating press operation completes in this way. This machine is applicable to dewatering of bean dreg, cassava dreg, starch alike.