In order to investigate the impacts of nitrogen (N) deposition on species diversity and community composition of herbaceous vegetation in desert steppe,we conducted a simulative N deposition experiment at ambient environment by adding N fertilizer into the plots in Shapotou area,northern China.We set four levels of N addition,0,6,12 and 24 g·m^-2,the different levels of N were singly added in the first year and then none for the following two years.The results indicated that both plant species diversity and community abundance decreased with the increase of N addition levels at a given year,especially,community abundance showed the greatest decline compared to the species diversity.The interannual variations of both species diversity and community abundance showed a similar phenomenon that the difference among the levels of N addition was significant under the low levels of N addition,but nor for the high levels of N addition.N deposition changed plant community composition of herbaceous vegetation layer in desert steppe,and the perennial forbs were more sensitive to be lost under N enrichment in contrast to perennial grasses,and finally the transformed community was dominated by fewer dominate species.It can be concluded that N deposition would reduce species diversity,change community composition of herbaceous vegetation,and the impacts of N deposition on desert ecosystems would not be eliminated immediately when N enrichment ceased.