A strain N3 with strong nitrogen fixation ability was selected from the farmland soil in Taian, Shandong Province and was identified as Bacillus megaterium based on the morphological, physiological and biochemical characteristics and 16S rDNA gene sequences analysis. Its nitrogenase activity was up to C₂H₄ 28.33 nmol/(h·ml). Four treatments were set to explore the inoculation effect of different plant growth-promoting bacterium on the growth of Orychophragmus violaceus, including single or double inoculation of strain N3 or IAA (indole-3-acetic acid)-producing stain Pantoea agglomerans CDL29, plant without any inoculation set as the control treatment (CK). The pot experiment of Orychophragmus violaceus was conducted under greenhouse conditions. The results showed that all plant growth-promoting bacteria promoted the growth of Orychophragmus violaceus, and the treatment with single inoculation of nitrogen-fixing strain N3 was the best. At the same time, nitrogen and phosphorus contents in the shoots of Orychophragmus violaceus, nitrogen and potassium contents in the roots of Orychophragmus violaceus were significantly increased by the single inoculation of nitrogen-fixing strain N3, which were increased by 33.03%, 55.56% and 29.87%, 51.11% respectively compared with CK. Other treatments also promoted nutrient contents in Orychophragmus violaceus, but the trends were not statistic significant. The contents of soil organic matter, total nitrogen and available nutrients were significantly increased by single inoculation of nitrogen-fixing strain N3. The contents of soil microbial carbon(MBC) and microbial nitrogen(MBN) were increased by the inoculation of different plant probiotics, single inoculation of nitrogen-fixing strain N3 had the best effect, followed by the single inoculation of IAA-producing stain CDL29 and compound inoculation. In addition, inoculation of nitrogen-fixing strain N3 significantly increased soil nitrogenase activity, while inoculation of CDL29 had no significant effect on soil nitrogenase activity. As a conclusion, the single inoculation of nitrogen-fixing strain N3 could significantly promote the growth, nutrient contents in Orychophragmus violaceus, and also improve the physicochemical and biological properties of the soil.