The invention provides a preparation method of 3-hydroxymethyl-7beta-phenylacetyl-3-cephalo-4-diphenylmethyl carboxylate. The invention uses 7-ACA as starting material and uses the technical route of acetylation of first 7-amino phenylacetyling and then removal of 3-acetylation by hydrolysing via alkali to prepare intermediate 3-hydroxymethyl-7beta-3-cephalo-4-carboxylate, avoiding generation of 3-O-phenylacetyl side products without protecting process and deprotecting process. During the preparation process of 4-diphenylmethyl-acrylation of intermediate, the ethyl acetate solution of diphenylmethyldiazomethane is directly added into the mixed solution after the hydrolysis reaction and the hydrochloric acid is dripped to accelerate the esterification reaction, avoiding the generation of lactone of 3-hydroxymethyl-7beta-3-cephalo-4-carboxylate and promoting the generation of methyl-esterification of diphenyl. The target product is washed by reflowing in acetone and the purity thereof is greater than 99%. The invention has the advantages of simple operation, moderate reaction conditions, high yield, high purity of the product, etc.