A method for producing water treatment agent polyaluminium chloride from industrial waste residues comprises the following steps: (1) calcining the admixture of bauxite, kaoline and coal slack for 2 to 4 hours; (2) crushing and screening; (3) adding 10 to 25 portions of screenings by weight into a reaction vessel and adding 15 to 25 portions of mixed waste acid liquor by weight; (4) agitating andheating to 100 to 150 DEG C for 2 to 5 hours; (5) adding 10 to 25 portions of the admixture of sulfur-iron slag, fly ashes and aluminum ashes by weight and simultaneously adding 20 to 35 portions of mixed waste acid liquid or 1 to 5 portions of sodium hypochlorite by weight; (6) heating to 80 to 130 DEG C for 2 to 4 hours; (7) heating 3 to 10 portions of calcium oxide saturated solution by weight, agitating and heating to 70 to 100 DEG C, and polymerizing for 1 to 3 hours; and (8) evaporating and filtering, and obtaining the water treatment agent polyaluminium chloride with the pH value of 3.0 to 5.5. The invention has the advantages of wide raw material source, simple process and lower cost.