Response patters were investigated for seedlings of Hedysarum mongolicum, a dominant shrub in Maowusu sandland, to the simulated precipitation change by artificially controlling water supply at four levels. Plant growth characters, in terms of branch number and length, leaf number and area, and biomass, increased while water supply increased. However, the effect of water supply on leaf photosynthetic rate was not significant. Root/shoot biomass ratio significantly decreased with the increase of water supply, which was considered adaptive distribution of biomass investments in the different water supply. Water supply obviously affected branching patter. Branch section number, branch number and length of the same section enhanced as water supply increased. Branch number and length were clearly positive correlation with total and aboveground biomass in four water supply treatments. Branch character fully showed plant growth.