The invention belongs to the technical field of primary lithium batteries, and discloses an impurity removal method for a positive active material of a lithium-ferrous disulfide battery. The method comprises the steps as follows: the positive active material containing ferrous disulfide powder is provided; the positive active material is extracted by an organic solvent; impurities are removed from the positive active material; the active material is subjected to vacuum drying; and an organic solvent is glycol dimethyl ether and/or 1,3-dioxolame. The impurities in the positive active material of the lithium-ferrous disulfide battery are extracted directly by a solvent component for preparing electrolyte, so that a new impurity is not introduced into the battery; the positive active material does not contact a lot of water to generate a Fe<2+> or Fe<3+> impurity; the extracted positive active material can be directly used after being dried; the problems that the electrical property, the storage property or the safety performance and the like of the battery are not affected by adding an additive to the battery are overcome; and the impurity removal method is relatively economical and applicable.