The invention discloses a preparation method for an aliphatic water reducer compounded with a polycarboxylate superplasticizer, which belongs to the field of concrete additives. The aliphatic water reducer prepared in the invention has anti-mud effect and can be compounded with the polycarboxylate superplasticizer at any ratio; the compounded aliphatic water reducer has obviously better performance, enables concrete to have better slump retention ability and strength under the condition that a doping amount is not changed, prolongs the service life of the concrete and overcomes the problems of poor dispersibility and fast slump loss of the polycarboxylate superplasticizer due to high mud content of aggregate of the concrete; raw materials used in the invention are widely available; and the preparation method is simple, free of emission of pollutants like waste gas, waste water and industrial residues, and suitable for industrial large-scale production.