A multifunctional concrete intensifier is prepared by a method comprising the following steps: at first, adding polyethers and 70%-75% of deionized water in a reaction vessel according to proportion; when heating to 55-65 DEG C, dropwise adding acrylic acid and an initiator in the reaction vessel and then cooling to 35-45 DEG C, adding caustic soda for neutralizing, stirring for 10-20 min to enable the components to be mixed uniformly to prepare a mixture I; adding triethanolamine, a surfactant and a thickening time control agent in the rest of 25%-30% of deionized water, and sufficiently stirring for 0.2-1 h at 35-45 DEG C to prepare a mixture II; then maintaining the temperature of the mixture I to 35-45 DEG C, stirring and slowly pouring into the mixture II, and sufficiently mixing for 0.5-1.5 h to obtain a light yellow liquid not easy to precipitate. The multifunctional concrete intensifier is chloride-free, is qualified in stability, meanwhile, has multiple functions of saving the comprehensive cost of concrete, improving the concrete workability, and increasing the concrete strength and the like, meets the national harmful substance requirement standard, reduces the cement content, and is simple to use, low in mixing amount, and small in investment.