Abstract: The present invention disclosed a concrete water reducer by grafting of lignosulfonate with carbonyl aliphatics and its preparation method. A technical solution of the method is as follows: compound proportioning of the concrete water reducer (weight) is: carbonyl group aliphatics:lignosulfonate=1:(0.75-1). The said concrete water reducer by grafting of lignosulfonate with carbonyl aliphatics is prepared through following process steps: controlling the temperature of aliphatics water reducer at 95-100° C.; dropping lignosulfonate into said aliphatics water reducer; conducting graft copolymerization reaction at 95° C.-100° C. for 2-5 h and obtaining lignosulfonate modified and grafted aliphatics concrete water reducer. The method of present application is simple, low cost and friendly to environment. The water reducer has good water reducing effect and can reduce colour aberration of concrete and thus be applied broadly.