The invention relates to a method for preparing a modified aliphatic high-efficiency water-reducing agent by utilizing lignosulfonate, belonging to the field of concrete water-reducing agents. The invention adopts acetone and formaldehyde as condensation monomers and lignosulfonate as a modifying agent and carries out sulfonating and condensation reactions under an alkaline condition to produce anovel high-efficiency concrete water-reducing agent. The preparation method of the novel high-efficiency concrete water-reducing agent comprises the following steps: (1) adding a sulfonating agent, acetone and water to a reactor, increasing the temperature to 25-65 DEG C and reacting for 0.1-1.5 hours; (2) dipping part of formaldehyde solution for 0.25-2.5 hours, increasing the temperature to 70-95 DEG C and reacting for 1-6 hours; and (3) decreasing the temperature to below 60 DEG C, adding the lignosulfonate and the rest of the formaldehyde solution to the reactor, using an alkaline regulator to regulate a pH value of the system to be 8.0-14.0, increasing the temperature to 70-98 DEG C, reacting for 1-5 hours and decreasing the temperature before discharging. The modified aliphatic high-efficiency water-reducing agent is suitable for producing commercial concrete which has similar color as normal concrete and has smaller collapsed slump loss. By adjusting the process, such as proportioning raw materials, and the like and effectively utilizing the lignosulfonate, the invention not only decreases the product cost, but also lessens environmental pollutants and has favorable industrialized prospects.