When the spiral sand washing machine is working, the crushing and grading materials are first passed through the conveyor belt to the double spiral sand washing device. After the grading and cleaning, the qualified material is dehydrated into the dewatering device, and the remaining waste water that after cleaning by the spiral sand washing device (containing a part of qualified material) is passed through the overflow device and get into the water reservoir device, then the waste water is pumped into the separation recovery device by slurry pump, material is concentrated under the action of centrifugal force, and the concentrated material get into the dehydrating device for dewatering.