The invention discloses a preparation method of high-purity cefotetan disodium for injection, belonging to the process fields of production and purification of cephalosporin antibiotics. The preparation method comprises the steps of carrying out acylation reaction, hydrolysis reaction and condensation reaction on the main raw materials including 7-MAC, an acylating agent and isothiazole mono-sodium salt, carrying out purification and impurity removal by virtue of an activated alumina chromatographic column, and carrying out the steps of decoloration, salt formation, refining and the like, so as to prepare cefotetan disodium. According to the preparation method, the quality risks caused by residual solvent residues and resin-free crushing can be overcome, the product quality is relatively good, and the impurity content is relatively low; and furthermore, the preparation method is relatively low in cost, simple in operation, saving in energy, environmentally friendly and suitable for industrial production.