The invention discloses a polyaluminum silicate iron-acrylamide copolymer composite flocculant and a preparation method thereof, which is characterized in that 20 parts of Na2SiO3 are added to 250 parts of deionized water, the pH value is 2 to 5, and the reaction is carried out at room temperature for 2 to 3 hours. Prepare activated silicic acid; use aluminum-containing waste, iron-containing waste hydrochloric acid and industrial hydrochloric acid to obtain mixed crystals of AlCl3 and FeCl2; add 1.2 to 25.0 parts of mixed crystals to 25 parts of activated silicic acid, react, stand and mature, and obtain poly Aluminum iron silicate PAFSI; add 20 parts of acrylamide, 75-450 parts of deionized water, 5-20 parts of ionic monomer, and 0.3-6 parts of macromonomer into the reaction bottle, stir, pH value 5-9, pass N2 , add 0.008-0.4 parts of potassium persulfate at 40-70°C, react for 12-36 hours, and prepare the copolymer PAME; add 100 parts of 5 g / L PAME solution into the reaction bottle, and add 12-350 parts under rapid stirring 100 g / L PAFSI solution, pH value 1-4, react at 30-40°C for 2-3 hours, then react at 50-75°C for 2-4 hours, and mature for 24 hours to prepare PAFSI-PAME composite flocculant.