A method for the synthesis of cefaclor using 7-amino-3-chlorinated cefacoalkanic acid and phenylglycine deng salt (ethyl sodium salt) as starting materials in a two-step process, characterized by the following steps:

1) mixed anhydride solution (mixed anhydride) was obtained by dissolving phenylglycine deng salt (ethyl sodium salt) and terpenyl chloride (trimethylacetyl chloride) in polar aprotic organic solvent under the action of pyridine catalyst.

2) 7-acca forms salt with nitrogenous organic base and dissolves in polar aprotic organic solvent to obtain 7-acca solution;

3) acylation condensation reaction was carried out between 7-acca solution and mixed anhydride under the condition of pyridine catalyst, and inorganic acid was added into the solution for hydrolysis, and the aqueous solution of cefaclor and acid salt was obtained by phase separation;

4) adding DMF or DMAC into the aqueous solution of cefaclor and acid salt to prepare cefaclor DMF or DMAC solvents under the condition of adding alkali;

5) cefaclor was obtained by conversion of DMF or DMAC solvents in aqueous and aqueous homogeneous organic solutions. The yield of cefaclor DMF complex reached 90%, and the total yield reached over 82%.