The invention discloses a method for preparing small-sized nanometer silver crystals through a blending-soaking-crystallizing method. The method includes the steps of firstly, evenly mixing sodium alginate powder with silver salt and solid reductant in a blending device; secondly, slowly soaking materials in deionized water, and conducting controlling to prevent water leakage in the soaking process; thirdly, keeping moisture in a sealed mode, conducting a reaction statically for 1 hour to 48 hours, and preparing semi-dry materials; fourthly, dissolving the semi-dry materials in an alkaline chlorine dioxide solution till the semi-dry materials are completely dissolved; fifthly, conducting refiltering or high-speed centrifugation, and then obtaining single-substance silver crystals as the main product and low-molecular-weight sodium alginate as the auxiliary product. The method is simple and controllable in process; the prepared nanometer silver has the advantages of being small in size, narrow in granularity distribution range and excellent in nanometer effect. The main product, namely, the silver crystals, is suitable for modifying electrically-conductive antistatic and antibacterial materials or manufacturing fiber modified through the spinning method; the auxiliary product is recycled to be used as fertilizers.