The invention relates to a method for preparing a cement additive by using AES sulfonated electrostatic demisting waste liquid. The method provided by the invention can be used for solving the problem of electrostatic demisting liquid during the production of AES. The technical scheme of the invention is as follows: the method comprises the following steps: (1) preparing an electrostatic demisting neutralization solution; (2) adding sodium silicate, sodium polyphosphate, sodium lignosulphonate, triethanolamine, diethylene glycol and ethanol diisopropanol into the neutralization solution, and uniformly stirring. The method for preparing the cement additive by using the AES sulfonated electrostatic demisting waste liquid comprises the following steps: (1) preparing an electrostatic demisting neutralization solution; (2) sequentially adding sodium silicate and sodium polyphosphate into the neutralization solution, and uniformly stirring at normal temperature and normal pressure; (3) adding sodium lignosulphonate and diethylene glycol, and continuing to stir uniformly at normal temperature and normal pressure; (4) finally, adding triethanolamine and ethanol diisopropanolamine, and stirring and mixing uniformly at normal temperature and normal pressure.