PURPOSE:To provide a method and a device capable of dehydrating sand in two-stage times and of being easily maintained. CONSTITUTION:The dewatering bottom part of a dehydration basket 2 is formed by stretching a dewatering network 25 and a filter cloth 26 on the opened bottom face. A plurality of dehydration baskets 2 are stuck to an endless chain at the proper intervals by connecting the dewatering bottom part sides to the chain. A raw liquid supply tank 4 is provided which supplies raw liquid containing sand to the hydration baskets 2. A detection switch 55 for detecting deposition of sand in the dehydration baskets 2 is provided and the endless chain is intermittently travelled. An air cylinder 61 closes the upper face of the aperture of the dehydration basket by a cover 64 in the next transfer position. An air force-feeding device force-feeds compressed air into the dehydration basket 2 by arranging an air nozzle 71 in the cover 64. A sand receiving tank 8 is provided in the reverse part of the endless chain. Raw liquid containing sand is supplied to the dehydration basket and naturally dewatered. The aperture of the upper face of the dehydration basket is closed and compressed air is force-fed into the dehydration basket to forcedly dewater sand. Dewatered sand falls from the dehydration basket in the reverse part and is discharged.