When operating, the motor drives the impeller slowly rotating through the V-belt and reducer. The sand is put into the washing tank through the feeding chute, and rolls over by the impellter driving. During the rolling, the friction between the sand particles strips the impurities, and breaks the vapor coatings around the particles in order to facilitate dehydration. Meanwhile, massive water is put into the washing tank to form a strong water stream to take the impurities and small percentage of foreign matters away immediately and discharge them from the overflow port. The clean sand is taken by the impeller, and finally puts into the discharge groove, finishing the whole washing process.