The invention discloses a combined treatment method of a waste lithium ion battery negative electrode and a diaphragm; the combined treatment method comprises the following steps of (1) carrying out crushing on the waste lithium ion battery negative electrode and the diaphragm, performing mixing to obtain mixed fragments, wherein the mass ratio of the negative electrode to the diaphragm is 5-10: 1; (2) putting the mixed fragments into a mixed solvent, stirring for 3-6 hours at the temperature of 70-140 DEG C, separating and recovering a copper foil from the solution, carrying out ultrasonic treatment on the residual solution at 0-70 DEG C, and separating to obtain a solid and a filtrate, and returning the collected filtrate to the step (2) to be repeatedly used as a solvent; and (3) carrying out high-temperature carbonization on the solid in an inert atmosphere to obtain the composite carbon material. According to the method, the high-additional-value utilization of the carbon materialand the diaphragm of the waste lithium ion battery can be realized, meanwhile, the copper foil can be recycled in an elementary substance form, the operation is simple, the cost is low, the environment is protected, and the like.