The impacts of different water supply conditions in different growth stages on tomato irrigation amount, net photosynthrtical rates, root distribution, yield and water use efficiency were analyzed through field experiment. Results show that the yield can attain 91.7 t/hm² and the water use efficiency reaches 27.51 kg/m³ when the lower limit are 60% and 75% of the field capacity at the flowering and fruit bearing stage, fruit stage, respectively. The total root length, surface area, volume, net weight and root length density significantly increases under this lower limit treatment. The highest net photosynthrtical rates occurrs under 75%fc. The density of root length declines exponentially with the increase of the soil layer depth. Different water conditions influence the growth of tomato root obviously. A good correlation between tomato yield and the ratio of the root length with diameter of less than l mm is better.