The invention discloses a method for preparing fluoro olefin, which comprises that: a perfluoro straight chain or branched chain acyl fluoride compound reacts with trifluoro vinyl ethyl sulfate in an organic solvent under the action of a catalyst so as to form a product having a general formula shown by the formula (I). The method avoids a pyrolysis route and uses no unconventional monomers, the used trifluoro vinyl ethyl sulfate can be prepared at a yield of above 95 percent, and a fluoro olefin monomer is prepared easily through an addition reaction, and a high-purity monomer can be obtained through rectification. CF2=CF-O-Rf (I).