The invention discloses a method for preparing a nanometer silicon negative electrode material by using waste silicon slag of photovoltaic industry. The method comprises the following steps: crushingthe collected waste silicon slag to obtain waste silicon powder; By acid washing, water washing and drying, the waste silicon powder can be purified at one time. The waste silicon powder after primarypurification was pulverized to less than 2 mm, and then calcined in an inert atmosphere to achieve secondary purification. Subsequently, the nanometer silicon suspension is obtained through the treatment of the coarse powder and the fine powder; and the nanometer silicon negative electrode material can be obtained by spray drying the nanometer silicon suspension. The method is simple, low cost, and can be industrialized, and can realize the resource utilization of a large amount of silicon waste. The first discharge capacity of the nano-silicon anode material is as high as 3305 mAh/g, and thecoulombic efficiency is 88.5%, which is superior to that of the nanometer silicon negative electrode material on the market.