The invention discloses a method for regenerating a positive active material from waste lithium iron phosphate batteries. The method comprises the steps as follows: 1) waste lithium iron phosphate batteries are discharged in saline water, and organic solvents, roll cores and casing materials are disassembled; 2) the roll cores are subjected to crushing, calcination and other steps, and active materials, copper foil and aluminum foil are separated through vibrating screening. Fluorine-containing waste gas is absorbed with lime water, the copper foil and the aluminum foil are separated with a magnetic separation method, the active materials are leached out with sulfuric acid, and a leachate and carbon residues are obtained through separation; 3) Cu<2+> in the leachate is reduced to elementary copper by adding iron powder, meanwhile, Fe<3+> is reduced to Fe<2+>, copper and excessive iron residues are filtered out, aluminum is removed through precipitation with an alkaline liquid, the filtrate is supplemented with a phosphorus source after filtration, the pH value is adjusted by adding the alkaline liquid, coarse lithium iron phosphate precipitates are produced, and finally, battery-grade lithium iron phosphate is obtained through sintering. Comprehensive utilization of the waste lithium iron phosphate batteries and regeneration of the active materials are realized with a simple, practical, economical and feasible method, no secondary pollution is produced, and the method is suitable for industrial production.