The invention discloses a method for extracting lithium from a waste lithium ion battery. The method comprises the following steps: performing reduction roasting on an active battery material separated from a battery current collector so as to obtain a reduction roasting material; performing carbonation leaching on the reduction roasting material, and filtering to obtain carbonation leaching residues and carbonation leaching liquor; removing cobalt from the carbonation leaching liquor, and filtering so as to obtain cobalt removing residues and cobalt removing liquor; heating and decomposing the cobalt removing liquor, and filtering to obtain a lithium carbonate-containing solid and decomposed liquor; circulating the decomposed liquor into the step B to serve as leaching liquor subjected tocarbonation leaching so as to be repeatedly utilized. The method disclosed by the invention is short in lithium recovery process flow, simple in operation, high in lithium recovery rate, high in lithium product purity, small in wastewater amount, small in reducing agent amount and low in recycling cost.