The invention discloses a preparation method of meropenem side chain disulfide. The method is characterized by comprising the following step that oxidative dehydrogenation reaction is performed in oxygen atmosphere by using meropenem side chains shown as the accompanying diagram as raw materials and using ferric trichloride as a catalyst to obtain the product of meropenem side chain disulfide. The preparation method has the advantages that the meropenem side chains are used as raw materials; a synthesis process of meropenem is skillfully applied to the preparation of an impurity intermediate of meropenem side chain disulfide; the process is obviously optimized through experiments; the impurity intermediate with the purity greater than 97 percent is obtained. The impurity intermediate with high purity is applied to the production monitoring of meropenem medicine; great convenience is provided for production of meropenem medicine and an intermediate of the meropenem medicine.