The invention relates to a water reducing agent for super slump retaining concrete, which is prepared from the following raw materials: 20-35% of polycarboxylic acid water reducing agent, 6-14% of polycarboxylic acid slump retaining agent C series, 1-4% of a retarder, 0.05-1% of a water retaining agent, 0.05-0.25% of an air entraining agent, 0-0.1% of a defoaming agent and the balance of water, wherein the sum of the mass percentages of the components is 100%. The polycarboxylic acid slump retaining agent C series is one or a combination of more than one of a polycarboxylic acid slump retaining agent C1, a polycarboxylic acid slump retaining agent C2 and a polycarboxylic acid slump retaining agent C3; the retarder is one or a combination of more than one of sodium gluconate, white granulated sugar, sodium tripolyphosphate, sodium hexametaphosphate, citric acid, oxalic acid, hydroxyethylidene diphosphonic acid, sodium citrate, tannic acid and zinc sulfate. The invention further providesa preparation method of the polycarboxylic acid slump retaining agents C1, C2 and C3. The water reducing agent can achieve long-term slump protection of the concrete, and solves the problems that theconcrete needs long-term slump protection in the concrete, but the concrete returns for a short time to seperate water, the setting time is not up to the standard, and the like.