Soil nematodes are widely used as an indicator of the function and stability of terrestrial ecosystems. The experiments were conducted in April 2021, Hongyuan county, Northwestern Sichuan to reveal the effects of nitrogen addition on the ungrazed and grazed alpine meadows. The gradients of nitrogen additions included 0 g/m², 20 g/m², 40 g/m² and 60 g/m². Soil nematode communities and soil properties were surveyed in September, 2021 and 2022. The results showed that: (1) the taxonomic composition and trophic structure of soil nematode communities in the grazed and ungrazed alpine meadows changed during the two continued years of nitrogen addition. (2) The nematode abundance was significantly lower, while the taxonomical richness and Shannon index were significantly higher in the ungrazed than grazed alpine meadows. The taxonomical richness and Shannon index significantly decreased in ungrazed, but significantly increased in grazed alpine meadows with increasing year. (3) Two continued years of nitrogen addition significantly increased the abundance of fungivores, but significantly decreased the abundance plant-parasites in the grazed and ungrazed alpine meadows, leading to the dominant trophic groups shifted from the bacterivores and plant-parasites to the bacterivores and fungivores. (4) The basal index of nematodes was significantly lower, but the maturity index and structure index were significantly higher in the ungrazed than the grazed alpine meadows. The basal index and channel index decreased significantly, and enrichment index and structure index increased significantly with increasing year in the grazed alpine meadows, with no significant changes observed for the ecological index of nematode communities with increasing year in the ungrazed alpine meadows. The study shows that nitrogen addition can promote the nematode diversity and soil food web stability in the grazed alpine meadows. Therefore, an appropriate amount of nitrogen fertilizer can be added to the grazed alpine meadows.