A knapsack automatic electric fertilizer spreader relates to a fertilizer spreading machine. The bottom of a charging bucket is provided with a bottom hole, the upper end of a material guiding tube is arranged in the bottom hole, the material guiding tube is fixed by a flexible fixing device, the material guiding tube is an L-shaped structure, and the corner of the material guiding tube is an arc transition; the structure of the flexible fixing device is characterized in that the internal diameter of a leather pad is consistent with the external material of the material guiding tube, the leather pad is tightly hooped to the material guiding tube, the upper mouth of the material guiding tube is provided with an abducent tube edge, a protection pad is arranged below the leather pad, the internal diameter of the protection pad is greater than the external diameter of the material guiding tube, and the protection pad and the leather pad are fixed to the bottom of the charging bucket through screws; the outer tube wall of the material guiding tube close to the tube edge is provided with a screw matching with a screw sleeve sleeved on the material guiding tube; and the material guiding tube is connected with the charging bucket through a telescopic rod. The knapsack automatic electric fertilizer spreader has wide adaptability and comprises unpowered spray and electric spraying cases, and the efficiency of the spreader provided by the invention is several times to dozens of times the efficiency of manual work.