1 Extreme events such as extreme drought and rainfall are predicted to be more frequent under ongoing climate change. Biomass allocation is an important strategy for plants to respond to such changes. However, few studies explored the effects of water availability on biomass allocation of dominant plants in Inner Mongolia steppe in China. 2 A controlled experiment was conducted by treating four perennial plant species (Leymus chinensis, Stipa grandis, Artemisia frigida and Potentilla acaulis) with eight levels of water availability, which was selected based on the local annual mean precipitation, simulating rainfall scenarios facing climate change. 3 Water availability significantly affected the aboveground biomass, belowground biomass, total biomass and the ratio of belowground biomass and aboveground biomass of plants, and these effects were modified by species. Our results indicated that plants could modify their biomass allocation strategies to adapt to the gradient of water availability. 4 Climatic factors such as precipitation and temperature always co-vary, thus responses of plants to more complicated climate change (e.g. the joint variation of temperature and rainfall) should be further explored in order to better understand grassland management and restoration under climate change.