Excessive nitrogen fertilization in sweet potato cultivation poses significant ecological and economic challenges in China, negatively impacting soil health by altering microbial community diversity, enzyme activities, and increasing the risk of stem nematode damage. In this study, we conducted a field trial in Northeast China, applying 0-72 kg of urea-N per hectare to brown soil under a five-year sweet potato cropping system. The results demonstrated that optimal nitrogen fertilization (64.8 kg ha-1) significantly promoted beneficial microbial populations, enhanced soil urease activity, and reduced the incidence of stem nematode disease while maintaining high sweet potato yields.