The invention discloses a preparation method of a poly carboxylic acid water reducing agent with a regular sequence structure. The preparation method comprises the following steps of performing Michael addition reaction on a polyethylene glycol ester acrylate macromer A and amino group containing carboxylic acid B for 5-12h, then cooling the temperature to 0 DEG C, dropwise adding acryloyl chloride slowly at a constant speed, and continuously performing reaction for 12h under the condition with normal temperature after dropwise addition is finished to obtain a carboxyl group containing polyether macromer C; and fully mixing the carboxyl group containing polyether macromer C, a small molecular RAFT reagent, an initiator and water, keeping the polymerization mass concentration be 30-60 percent, rising the temperature to 60-80 DEG C at the atmosphere of N2, and performing reaction for 2-5h to obtain the poly carboxylic acid water reducing agent with the regular sequence structure. The poly carboxylic acid water reducing agent prepared by the preparation method is suitable for regions with high mud content of sandstone aggregates and has the advantages of low mixing amount, high waterreducing ability and high slump loss resistance. The preparation method provided by the invention is simple in preparation technology as well as is environmentally friendly and is low in cost in the production process.