The invention provides a preparation method of a benzoic acid derivative. The method comprises the following step: hydrolyzing a cyanobenzene derivative in an aqueous reaction mixture to generate the benzoic acid derivative under the action of an enzyme catalyst containing nitrilase, preferably, wherein the cyanobenzene derivative is selected from ammonia methyl cyanobenzene and chlorine methyl cyanobenzene; preferably, the nitrilase is an amino acid sequence of which the number is ABD98457.1 in GenBank. By adopting the method, paraaminomethyl benzoicacid and p-chloromethyl benzoic acid can be efficiently produced, and the method is mild in reaction condition, friendly to environment, simple and convenient to operate. The method for producing the benzoic acid derivative by biological catalysis provided by the invention has a good industrial application prospect.