In order to investigate the mechanism of the Chaetomium globosum ND35 microbial agent on the growth and soil fertility of Catalpa bungei seedlings, the C. bungei seedlings were taken as the research object and 0, 10, 15, and 20 g microbial agents were applied on the C. bungei seedlings' root. And the growth status of the seedlings, the composition structure of soil microorganisms, soil enzymes and soil nutrients were measured. The results were obtained as follows:(1) the C. globosum ND35 could significantly promote the growth of C. bungei seedlings. The plant height, ground diameter, aboveground and underground biomass were significantly increased (P<0.05). And there was a best promotion effect at T2. (2) The contents of organic matter, nitrate nitrogen, ammonia nitrogen and the activity of urease, phosphatase and sucrose enzyme in soil were significantly improved by applying the C. globosum ND35 microbial agent (P<0.05). (3) The composition of soil bacterial communities was significantly influenced by C. globosum ND35. And the diversity of soil bacterial communities was also increased significantly. The relative abundance of Betaproteobacteria and Gammaproteobacteria were significantly declined after using C. globosum ND35. And the relative abundance of Alphaproteobacteria, Deltaproteobacteria, Sphingomonas, Bacillus, Acidibacter were significantly improved. Among them, the relative abundance of Sphingomonas, Bacillus, Acidibacter increased 21.88%-103.56% (P<0.05), 66.28%-65.97% (P<0.05), 12.76%-38.06%, respectively. (4) Redundancy analysis (RDA) ascertained that the distribution and diversity of bacterial communities were closely related to the organic matter, nitrate nitrogen and ammonia nitrogen. And the activity of urease, sucrase and alkaline phosphatase were significantly altered with the change of soil bacterial community structure. Therefore, applying C. globosum ND35 microbial agent could promote the growth of C. bungei seedlings by affecting the chemical and biological properties of rhizosphere soil. The results could provide a new direction for the breeding of C. bungei seedlings and theoretical guidance for the C. globosum ND35 microbial agent application in vegetation restoration of degraded ecosystems.