Abstract: By using nutrient solution culture and simulated water stress by PEG(6000),the effects of different nitrogen forms(NO3--N, NH4+-N and the mixture of NO3--N and NH4+-N) and water statuses(non-water stress and water stress) on water use efficiency(WUE) and the biological characteristics of rice plants at seedling-tillering stage were studied.The results showed that,under non-water stress,the biomass of rice plants were about 49.63% and 63.25% higher under the supply of mixture of NO3--N and NH4+-N than either sole supply of NO3--N or NH4+-N,respectively.However,under water stress,the biomass of rice plants were about 5.76% and 484.01% higher under sole ammonium supply than the other two treatments,WUE of rice plants were also 11.36% and 81.63% higher than the two treatments,while 12.39% higher than the same nitrogen form supply under non-water stress.Furthermore,rice plants grown with ammonium nutrition showed a stronger tolerance to water stress,due to their higher chlorophyll content,leaves area,tillers,and net photosynthetic rate et al.compared with those grown with nitrate nutrition.