The invention discloses preparation and application of bacillus megaterium BM22 and a liquid preparation of the bacillus megaterium BM22. The bacillus megaterium BM22 is preserved in China General Microbiological Culture Collection Center on December 15, 2017; the preservation number is CGMCC No.15070. The bacillus megaterium BM22 is used as a strain and can be prepared into a liquid preparation through seed culture and fermentation culture. The bacillus megaterium BM22 provided by the invention has the special effect on root rot and blight of magnolia officinalis roots, has stress resistance,good storage property, resistance to high temperature, resistance to low temperature and drying resistance, is applied to commercial production, is capable of avoiding the serious consequences of environment pollution caused by chemical drugs, and meets the national sustainable development strategy; compared with the chemical drugs, the bacillus megaterium BM22 also has the characteristic of lowcost.