The invention relates to a method of preparing 2,2'-dithiobis(benzothiazole) from 1,3-benzothiazole-2-thiol. The method includes dissolving the 1,3-benzothiazole-2-thiol into a methanol-trichloromethane mixed solvent, adding a catalyst that is tetrabutylammonium bromide, bubbling ozone at 40-45 DEG C, reacting under stirring for 1-1.5 h, allowing addition of the ozone to be stopped after the reaction is finished, continuously stirring, maintaining the reaction temperature for 1-1.5 h, cooling to 5-10 DEG C, filtering and drying under vacuum to obtain the 2,2'-dithiobis(benzothiazole). By adoption of the method, purification of the 1,3-benzothiazole-2-thiol (being called as M for short) is not needed, and the 2,2'-dithiobis(benzothiazole) (being called as DM for short) prepared through the reaction can meet standards on raw materials used for pharmaceutical production and can be directly used for synthetic reactions of AE-active esters or other pharmaceutical intermediates and pharmaceuticals. The method is simple in process, mild in conditions, safe and easy to control. The solvent used in the method is low in pollution, easy to recover and low in production cost. The method is suitable for large-scale production.