A method for preparing cathode material for a lithium primary battery includes an active cathode material and an active anode material. The active cathode material is manganese dioxide, and the active anode material is either one of lithium metal and lithium alloy. The method includes: a first kneading step in which a boron compound and a thickening agent are kneaded with a diluent to prepare a paste made by dissolving the boron compound in the diluent; a second kneading step in which the paste is kneaded with a conductive additive; and a third kneading step in which the paste obtained in the second kneading step is kneaded with the active cathode material and a binder to prepare the cathode material in slurry form.