The present invention relates to a high efficiency water reducing agent for manufacturing high performance cement based material such as high-strength concrete, fluid state and/or pumping concrete, etc. and method for preparing same. The invention takes ketones compound and aldehydes as condensation monomer, and sulphite as sulphonating agent, and take condensation reaction in alkaline aqueous solution. Then a water-soluble high-polymer condensate containing hydrophilic group such as sulfonic group, carboxy, hydroxyl, etc. in molecule with molecular weight ranging from 3000 to 10000 is obtained. By changing the matching, charging sequence of raw material, the technological process is simplified, the reaction time is shortened, and burst boiling and geling phenomena are also avoided at the same time. By controlling charging rate and condensation temperature, the condensation product is made with required molecular weight and can meet application performance. The fatty group sulphonate condensation compound made by the invention can be served as high efficiency water reducing agent of cement concrete, the water reducing, dispersion and reinforcing effects are better than the traditional albocarbon group high efficiency water reducing agent. The water reducing agent provided by the invention has the advantages of wide raw material source, simple synthesizing process, clean and suitable for industrial production.