The invention discloses a method for increasing the acetoin yield by means of vitamin B2. The method includes the following steps that seeds cultured by means of Paenibacillus polymyxa CJX-518 with the preservation number being CGMCC NO.7096 are inoculated into a fermentation culture medium according to the inoculation density that the biomass is 0.1-0.4, the seeds are fermented at 32-42 DEG C at the stirring rotation speed of 100-300 rpm, vitamin B2 with the density of 1-10 g/L is added when fermentation is conducted for 0-24 h, fermentation continues, and a fermentation broth containing acetoin is obtained; CJX-518 is cultured in the fermentation culture medium added with vitamin B2, and the acetoin yield can be increased.