The invention discloses a method for preparing an amphoteric ethylene base polymer water reducing agent. The method uses polyethylene glycol, methacrylic acid, maleic anhydride, citric acid, and the like as raw materials and prepares a high-efficiency amphoteric ethylene base polymer water reducing agent through an esterification reaction and a polymerization reaction. The method controls polymerbranched chains, the number of functional groups and relative molecular mass thereof by controlling process conditions and material feeding methods so as to finally regulate and control the performance of the amphoteric ethylene base polymer water reducing agent and obtain the high-efficiency amphoteric ethylene base polymer water reducing agent. Compared with the prior polycarboxylate type waterreducing agent, the amphoteric ethylene base polymer water reducing agent has good adaptability to cement, high water reducing rate and less intermingled quantity.