The invention provides a bacillus promoter for wastewater treatment and a preparation method thereof. The method is implemented by taking fruits as a fermentation substrate through the steps of material preparation and pretreatment; primary bacteria cultivation, and prior fermentation; secondary bacteria cultivation, and medium-term fermentation; coarse filtration, and late fermentation; deploying, and curing; fine filtration, concentration, filling and the like, so that a finished promoter product is obtained finally. The promoter provided by the invention can make bacilli become dominant bacteria in a biochemical reactor for sewage treatment, maintain the high activity of bacilli, and provide necessary trace elements for the germination and formation of bacillus spores.