Fertilization is one of the most common ways of human disturbance in the current grassland ecosystems, which can lead to changes in grassland biodiversity and ecosystem stability. At present, a few studies, however, have explored the effect of fertilization on community stability and the underlying mechanisms, but there are many controversies. For this reason, we took the typical steppe of the Loess Plateau as the research object, and through 8 consecutive years of field experiment of adding nitrogen fertilizer (urea), we studied different nitrogen fertilizer treatments (respectively 0, 5, 10, 20, 40, 80 g·m^-2) influence on the stability of the grassland ecosystem, and tested four underlying mechanisms (species diversity, species synchrony, portfolio effect, dominance) that may affect the stability of community, to clarify the impact of fertilization on community stability and its underlying mechanism thus providing a theoretical basis for the rational use of grassland restoration on the Loess Plateau. The results showed that: (1) as the fertilization level increased, the community stability (S) decreased, and it began to decrease significantly when the fertilization treatment was 20 g·m^-2 (P<0.01). (2) Fertilization significantly reduced the species richness (R) and dominance index (D) (P<0.01). However, the species synchrony (_B) and the meanvariance ratio index (z) did not change significantly (P>0.05). (3) There was a positive correlation between species richness (R) and community stability (S), while dominance index (D) was not correlated with community stability (S). Studies suggested that under the disturbance of fertilization, the decline in species richness of typical steppe on the Loess Plateau led to a decline in community stability, indicating that species diversity plays an important role in maintaining the stability of grassland ecosystem.