The invention relates to the technical field of lithium battery material recovery, and provides a method for recovering lithium in a ternary positive electrode material by microwave roasting, whereinthe method comprises the steps: mixing a waste ternary positive electrode material, diluted hydrochloric acid and an assistant, carrying out microwave roasting, carrying out ball milling and water leaching on the roasted product to obtain a lithium chloride solution, concentrating, crystallizing, carrying out solid-liquid separation, and drying to obtain lithium chloride. According to the method provided by the invention, conventional roasting is replaced with microwave roasting, materials are heated from inside to outside through microwaves, the roasting temperature is reduced, and the roasting time is shortened; ball-milling water leaching is adopted to replace crushing and water leaching or crushing and acid leaching in a traditional method, the water leaching process is accelerated through ball-milling water leaching, the leaching rate is increased, leachate hardly contains other high-valence metal ions, and lithium chloride can be directly prepared without purification and impurity removal.