<p>Root-knot nematodes (RKNs) are a threat to the growth of <i>Catalpa bungei</i>, an ornamental tree species native to China, in nurseries. This study investigated the potential use of arbuscular mycorrhizal fungi (AMF) to inhibit RKNs and the AMF-mediated physiological and biochemical responses against RKNs in <i>Catalpa</i> cultivars. We demonstrated that AMF significantly promoted plant growth and reduced nematode reproduction in the susceptible cultivar, the moderately resistant cultivar, and the resistant cultivar. A significant change in plant height was observed from the resistant cultivar (20.6-fold). AMF inoculation modulated root length and increased lateral branching of RKN-infected plants. Gas exchange traits and nutrient absorption were improved by AMF inoculation in nematode-infected plants, favoring enhanced photosynthesis. Peroxidase activity was increased in AMF-inoculated plants under nematode infection. The peroxidase activity of the resistant cultivar exhibited a significant change upon AMF inoculation. Additionally, AMF inoculation suppressed indole-3-acetic acid (IAA) and strigolactones (SLs) accumulation. AMF inoculation showed both inhibitory effects on nematode infection and promoted effects on plant growth. Among the three kinds of cultivars, AMF inoculation had a significant biocontrol effect on the resistant cultivar against nematode infection in the pot experiment. The effect of AMF inoculation is achieved via multiple mechanisms including direct inhibition of infection, modulation of root architecture and regulation of plant defense. This study highlights the protective role of AMF in plant defense to resist RKNs, offering a sustainable strategy for controlling RKNs in <i>C. bungei</i> cultivation.</p>