Responses of species composition and richness to global change remain a major uncertainty in alpine grassland.Here we performed a three-year manipulative experiment to examine the changes of community structure and species richness under three precipitation regimes(doubled,control and halved)and two nitrogen(N)addition rates[0 and 10 g/(m~2·year)]in an alpine steppe on the Qinghai-Tibetan Plateau.The main results are as follows.(1)N addition significantly reduced species richness from 24,25,21 to 21,21, 20 along the precipitation gradient.(2)N addition and precipitation treatments significantly influenced community cover,which increased with N addition and increase of precipitation.Meanwhile,precipitation also interacted with year to affect community cover,following the trend 2015>2014>2013 across the three precipitation gradient.(3)The Simpson index,Shannon-Wiener index and Pielou index varied significantly among years.N treatment substantially altered richness index,while changing precipitation regime had significant effect on Pielou evenness.Overall,N addition had significant influence on species composition, community coverage and richness index in this alpine steppe,while precipitation only influenced on coverage. Except that changing precipitation altered Pielou index,both precipitation changes and N addition had minor contributions to diversity index.