The present invention relates to the field of waste battery recycling, and discloses a method for treating waste diaphragm paper of a lithium battery, which includes the following steps of: (1) shearing and crushing waste diaphragm paper, and then carrying out pneumatic separation to obtain a light material and a copper-aluminum mixture; (2) putting the light material into a flotation machine for separation to obtain diaphragm paper and battery powder; and (3) pulping the battery powder, and then carrying out leaching of hydrometallurgy, pickling the diaphragm paper, and then filtering and spin-drying to obtain the diaphragm paper. According to the method, the diaphragm paper is treated by a method combining physics and chemistry, so that valuable metals in the waste diaphragm paper of the lithium battery are effectively recycled, and the industrial production requirements of environmental friendliness, low energy consumption and high resource recycling are satisfied.