The invention belongs to the field of medicine synthesis and specifically relates to a preparation method of an anidulafungin side chain intermediate 4'-orthopentyloxy-1,1':4',1'-terphenyl-4-carboxylic acid. The preparation method comprises the following steps: initiating a 1,4-dibromo-benzene material which serves as a starting material to carry out Grignard reagent reaction with magnesium by iodine; then, preparing 1,4-benzene hypoboric acid by virtue of addition and hydrolysis with trimethyl borate; and preparing 4'-orthopentyloxy-1,1':4',1'- terphenyl-ethyl carboxylate by virtue of Suzuki reaction of 1,4-benzene hypoboric acid, 4-pentyloxy bromobenzene and 4-halogenated ethyl benzoate in dioxane-ethanol liquor under catalysis of [1,1'-bis(diphenyl phosphino) ferrocene] palladium dichloride, and then, hydrolyzing to obtain a target product. The preparation method disclosed by the invention can lower process cost, is simple, convenient, safe and reliable to operate, and suitable for industrial production.