The utility model discloses a device for producing a water treatment agent polyaluminium chloride by using a waste reflective film. The device comprises an acid storage tank, a dealumination reactiontank, an anti-corrosion high-temperature-resistant net bag, an acid-resistant pump, a curing reaction tank and the like, the acid storage tank is placed at a high position to form acid liquid self-flowing; acid liquor enters the dealumination reaction tank through an acid liquor conveying pipe; putting the crushed reflective film into an anti-corrosion high-temperature-resistant net bag; during dealumination reaction, acid liquor is conveyed by the acid liquor return pipe under the action of the acid-proof pump to form reverse flow, when the concentration of metal aluminum in the return acid liquor meets the requirement, the return flow is stopped, the acid liquor enters the curing reaction tank through the conveying pipe until the curing reaction is finished, and then liquid polyaluminumchloride is discharged from the liquid discharge pipe through the discharge port. The dealumination efficiency of the device can reach 90% or above, chemicals do not need to be added, industrial acidand aluminum react to prepare the water treatment agent polyaluminum chloride, and the water treatment agent polyaluminum chloride conforms to the national standard. The device is reasonable in structure, high in automation degree, high in reaction efficiency, time-saving, labor-saving and environment-friendly in application.