The invention discloses a method for preparing water chestnut 
dry powder. The method specifically comprises the following steps: cleaning harvested 
water chestnuts, removing impurities and peeling the 
water chestnuts, thus obtaining water chestnut 
flesh and water chestnut peel; mixing the water chestnut 
flesh with water, pulping the mixture and carrying out filtering separation, thus obtaining water chestnut 
flesh residues and water chestnut pulp; mixing the water chestnut flesh residues with the water chestnut peel, 
grinding the mixture and sieving the 
powder, thus obtaining ground 
water chestnuts; mixing the ground water chestnuts with water and carrying out ultrasonic treatment, thus obtaining a water chestnut extracting solution; mixing the water chestnut pulp with the water chestnut extracting solution, concentrating the mixture till paste at reduced pressure and carrying out 
drying, 
grinding, sieving and sterilization, thus obtaining the water chestnut 
dry powder. Compared with the prior art, the method has the beneficial effects that the preparation process is simple and energy-saving and environment-friendly; the nutrients in the water chestnut residues and the water chestnut peel can be extracted through deep extraction treatment of the water chestnut residues and the water chestnut peel, thus avoiding waste and furthest retaining the nutrients in the water chestnuts; the prepared water chestnut 
dry powder is convenient to carry, has comprehensive nutrients, does not have chemical additives and is green and safe.