The invention provides a preparation method of a concrete water evaporation inhibitor. The obtained concrete water evaporation inhibitor is uniform in particle size and difficult in layering, and a use quantity of an emulsifier can be reduced. The preparation method comprises the following steps of preparing components of the concrete water evaporation inhibitor, wherein the components include C15 to C20 long chain alcohol, the emulsifier, water and selectable thickener and antifoaming agent; mixing the long chain alcohol, the emulsifier and water for pre-emulsification; in a state that the long chain alcohol is completely molten, carrying out high-speed shearing emulsification at a temperature above 40 DEG C, wherein mass of the water for pre-emulsification is 15 percent to 50 percent of all water consumption in the components; then rapidly adding the rest of water with a temperature of 5 to 30 DEG C in 1min, and carrying out high-speed shearing stirring to uniformly mix the components; selectably continuing to add the thickener and the antifoaming agent, and uniformly mixing to obtain the concrete water evaporation inhibitor.