Nitrogen (N) is a key element for plant growth of terrestrial ecosystems, and it is a commonly limiting factor for grassland productivity in semiarid grasslands. Nitrogen deposition has increased 2-5 times since 1950s. Some studies have documented that N deposition has positive effects on primary production or negative effects on biodiversity, soil nutrition etc; however, the results of previous studies are still inconsistent or even controversial. We designed a simulation nitrogen deposition experiment involved 9 N deposition gradients in Inner Mongolian grassland in 2008. Moreover, the experiment includes 2 N deposition frequencies (applied twice a year and applied every month equally) and 2 grassland management regimes (fenced grassland and mowing grassland). In this paper, we used the Chlorophyll content (SPAD value) of Leymus chinensis leaf, the dominant plant species in the region, in order to explore the effect of N deposition intensity and frequency and grassland management regimes on the structure and function of grassland ecosystem in Inner Mongolia. The results showed that 1) N deposition significantly increased leaf chlorophyll content; 2) the content of leaf chlorophyll in low N deposition frequency treatment was significantly higher than that in high N deposition frequency treatment; 3) the content of leaf chlorophyll was higher under mowing than under fenced, 4) leaf N concentration was highly consistent with leaf chlorophyll content, and 5) there existed positive linear relationship between plant height and leaf chlorophyll content. Totally, our finding first explored the effect of N deposition intensity and frequency and grassland management regimes on the structure and function of grassland ecosystem (in view of leaf chlorophyll content) in Inner Mongolia, and found that the low N deposition frequency (once per year or twice per year, as fertilization) should be magnified the effect of elevated N deposition in future. Therefore, we should be cautious to extend the results come from these low N deposition frequency to larger scale. Moreover, N deposition increased the leaf chlorophyll content and favored the primary productivity, and therefore can be better facilitated the grassland sustainable development in Inner Mongolia.