The invention relates to a preparation method of a polycarboxylate superplasticizer, belonging to the technical fields of building materials and cement concrete admixtures. The polycarboxylate superplasticizer is prepared by taking methylallyl polyethylene glycol and acrylamide as reaction monomers and sodium dodecyl sulfonate as a surface absorption activator, adding a chain transfer agent and an initiator, and finally, regulating the PH value to 6-7 by using an alkaline solution. The polycarboxylate superplasticizer is high in yield and good in performance; and due to the addition of sodium dodecyl sulfonate, the saturation rate of charges adsorbed by particles on a concrete surface can be increased, the flowability of cement in concrete stirring can be improved, the stirring time can be shortened, the efficiency can be increased, and an anti-adhesion effect is better taken. The polycarboxylate superplasticizer is simple in preparation process, low in cost, high in water reducing efficiency, good in cement and concrete compatibility and capable of effectively improving the flowability, slump constant, superstrength and durability of concrete.