The invention discloses a bacillus megaterium strain X3 and application thereof to plant growth promotion. The bacillus megaterium strain X3 is preserved in the China General Microbiological Culture Collection Center (CGMCC) on May 11, 2015 with the preservation number of CGMCC No.10803, is obtained through separation of indoleacetic acid, has the characteristics of siderophore production, phosphate solubilizing, ammonia producing, salt tolerance and disease suppression, can remarkably promote crop growth and improve corn yield, and meanwhile, can increase the diversity and the abundance of microbes in soil. The bacillus megaterium strain X3 is quick in reproduction, simple in production process, strong in adversity ability, easy to preserve and conductive to industrial production, and can not only prevent and cure soil-borne diseases but also promote plant growth when utilized to prepare a bio-fertilizer, thereby having a wide application prospect.