The invention discloses a rhizobium and microbial inoculum, preparation method and application thereof. The rhizobium is a Rhizobium radiobacter A32, the preservation department of the rhizobium is the China General Microbiological Culture Collection Center (CGMCC), the preservation date of the rhizobium is November 21, 2014, and the preservation serial number is CGMCC, No.10031. The rhizobium belongs to the kingdom of bacteria, the phylum of mycetozoan, the class of alpha-mycetozoan, the order of rhizobia, the family of rhizobia and the genus of rhizobia. The rhizobium is microbial inoculum which has active components and is obtained after plate culture, seed culture and fermentation are conducted on the radioactive rhizobium. Bacillus is microbial inoculum which has active components and is prepared through plate culture, seed culture, fermentation and fungicide preparation. The microbial inoculum is used for phosphate solubilizing and potassium solubilizing of soil and increase of the amount of soil mineral nitrogen.