In order to reveal the effects of irrigation volume on regulating tomato growth and quality，this paper studied the changing rule of tomato growth，leaf photosynthetic parameters，yield，quality and metabolism related enzymes under different irrigation volumes（2.0，1.6，1.2，0.8，0.4 L · d^-1）using rootlimited soiless cultivation system．The results indicated that reducing irrigation volume could significantly limit tomato growth，decrease net photosynthetic rate（P_n），transpiration rate（T_r），intercellular CO₂ concentration（C_i），stomatal conductance（G_s） ，single plant yield and single fruit weight．But，reducing irrigation volume could significantly increase the contents of glucose，fructose，and VC；improve acid-sugar ratio in fruits，and gradually increase the contents of soluble sugar and titratable acid．Reducing irrigation volume could also reduce the activities of sucrose synthetase and phosphate sucrose synthetase in tomato fruit；improve the activities of neutral invertase and acid invertase，resulting in the decrease of sucrose content．By combing entropy weight method with TOPSIS method，the paper analyzed comprehensively various indexes．The results showed that 0.8 L was the best daily irrigation volume for tomato under soiless cultivation．