Method for preparing polycarboxylic acid water reducing agent by using tail solution of producing acrylaldehyde

The invention discloses a method for preparing a polycarboxylic acid water reducing agent by using tail solution of producing acrylaldehyde. The method comprises the following steps of: dissolving unsaturated polyether into deionized water, stirring and heating, adding hydrogen peroxide when the temperature is raised to 30 to 50 DEG C, dripping mixed solution of acrylaldehyde tail solution and oxidant for 2 to 4 hours when the temperature reaches 60 to 80 DEG C, simultaneously dripping mixed aqueous solution of reducing agent and chain transfer agent, continuously preserving the heat for 0.5 to 2 hours after dripping is finished, then cooling the solution to the temperature of below 40 DEG C, adding aqueous solution of sodium hydroxide to neutralize the solution, controlling the concentration of the product to be 20 to 30 percent, controlling the pH to be 6 to 8, and finally obtaining yellow transparent solution; and performing reduced pressure distillation on the yellow transparent solution to obtain the pol