Abstract: The effects of CO2 elevated from 350 L/L to 800 L/L on the biomass,root characteristics and nutrient uptake of tomato seedlings were studied by carrying out a hydroponics experiment with conditions of P deficiency and normal P supply.The results showed that elevated CO2 significantly increased the dry matter accumulation of shoot and root,and root/shoot ratio of tomato seedlings no matter P was deficient or not.The effect of elevated CO2 on promoting root growth was mainly indicated by increase of root volume and surface area under P deficient conditions while by increase of not only root volume and surface area but also root forks under normal P supply conditions,which was beneficial to form a strong root system.Under both conditions of P deficient and normal P supply, elevated CO2 showed a diluting effect with different degrees on N,P and K contents in different organs of tomato plant.However,the total accumulation of N,P and K in tomato plant was markedly increased by elevated CO2.Moreover,an obviously significant positive interaction between CO2 concentrations and P supply on N,P and K accumulation in tomato plants was also observed.