The invention discloses a method and a device for recycling and harmlessly treating waste lithium ion battery electrolyte. The method comprises the following steps: step I, adequately discharging a waste lithium ion battery, and collecting cells; step II, placing a reaction tank with a solvent onto a magnetic heating stirrer, and carrying out the water-bath heating at the temperature of 50 to 90 DEG C; and step III, soaking the cells in the solvent; step IV: dropwise adding little water into a reaction solution, simultaneously adding lithium phosphate, controlling the stirring speed to be at 200 to 800r/min in the reaction process, wherein the reaction time lasts for 0.5 to 6 hours, generating a solution containing lithium difluorophosphate, introducing inert gas into the reaction tank, generating hydrogen fluoride in the reaction process, absorbing hydrogen fluoride by virtue of an absorption device, and recycling a process product-lithium fluoride by virtue of filtering. By adopting the method and the device, electrolyte salt and an organic solvent resource can be effectively recycled, the resource configuration can be optimized, the reutilization of the resources can be promoted, and energy can be saved.