The invention relates to a preparation technology of a rubber antioxidant, in particular to a preparation method of a rubber antioxidant MB (2-mercaptobenzimidazole). A synthesis process of regulating an acid-binding agent online is adopted, and 2,2'-ethylidene bis(4,6-di-tert-butyl) phenol, acrylic acid and phosphorus oxychloride are taken as raw materials to synthesize the rubber antioxidant MB. The preparation method provided by the invention has the advantages that pH of a reaction solution is regulated to be weakly alkaline and changed in a narrow range, yield of the rubber antioxidant MB product is high, quality of the rubber antioxidant MB product is good, production cost is low and industrial production is easy to realize.