The invention relates to the technical field of microbiological fermentation engineering, and aims to provide a method for preparing an insecticidal bioactivator. In the method, piericidin A is prepared by adopting microbiological fermentation technology. The method is characterized in that: an adopted producing bacterium is streptomucespiomogeues var.hangzhouwanensis which is collected in China general microbiological culture collection center (CGMCC). In the method, a fermentation culture medium of the invention mainly comprises the components of ordinary agricultural products, and a fermentation cycle is relatively shorter, so the preparation cost is relatively lower.