Rice (Oryza sativa L) had been traditionally recognized as the typical plant preferred NH₄⁺-N as its N source.But more and more reports have shown that plant growth and yield is superior on mixtures of NH₄⁺-N and NO₃^--N compared with provision of either nitrogen alone and only a few species actually perform well when NH₄⁺-N was provided as the only N source.NO₃^--N had become the important N source for rice crop cultivated in aerobic condition because of most the inorganic N in soil existed in this fom.To evaluate the effects of mixed nitrogen nutrition on growth and water use efficiency of rice cult ivated in aero-bic condition, a pot experiment was conducted under different rates of NH₄⁺-N and NO₃^--N application from 3-leaf stage to earring stage of the crop.The mixed nitrogen solution of NH₄⁺-N and NO₃^--N was carefully injected into Typicudi Alluuvic Primosols in potevery other two days at the ratio of 100/0,75/25, 50/50, 25/75 and 0/100.The amount of water irrigated everyday photosynthesis rate of functional leaves and yield of rice were measured and counted.The results showed that the total requirement of water by rice could be significantly reduced by proper application of NH₄⁺-N and NO₃^--N in aerobic cultivation.Meanwhile the photosynthesis of the functional leaves after earring was improved greatly and the dry matter and grain product ive efficiency of water by transpiration was raised by utilizat ion of NO₃^--N at a suitable ratio.The highest biomass production and maximum grain yield was obtained when 50% of nitrogen fertilizer as NO₃^--N was applied.Both root weight and ratio of root and shoot would be reduced when the proportion of NO₃^--N was ≥50%.