Abstract: Aimed at the raw water quality characterizd by low temperature and low turbidity in winter, high algae and organic matter in summer, the combined process of potassium permanganate pre-oxidation/ dissolved air flotation/ GAC-sand filter was developed to treat high algae water in Queshan reservoir. Test showed that the process could reach a better result when the dosage of potassium permanganate preoxidation was 0.3 mg/ L, the dosage of PAFC was 3 mg/ L (Al³⁺) , the dissolved air pressure was 0.3MPa and the recycle rate was 11%. The averaged removal efficiency of TOC, turbidity, particulate matter, chlorophyll a and blue-green algae by combination process were 46. 68%, 94. 45%, 99. 34%, 66. 64% and 95. 44%, respectively. Odor level decreased with process flow, from raw water level 4 to effluent level 1. 5. GSM treated by flotation unit was under the detection limit, and the removal efficiency of MIB reached 92. 47%. The removal rate of each component of THMFP, including CHCl₃, CHCl₂ Br, CHClBr₂ and CHBr₃, were 42.86%, 24.09%, 30.30% and 37.50%, respectively. The combined process has a good ability to remove regular indices, algae, odor substances and precursors of disinfection byproducts.