Abstract: This experiment was conducted for four years running(1981-1984)in our institute, at the testing pit under a movable rain shelter, in order to study the effect of soil moisture on the physiological function, yield and sugar content of sugarcane. The tests were carried out at the fast-growing stage(FGS)of the cane and the maturing-stage for cane processing(MSP).The tests at FGS indicate that 1)physiological functions such as chlorophyll content, intensities of photosynthesis and transpiration, ratio of free water and bound water, increase with soil water; 2)the increase shows a declining tendency when the water holding capacity(WHC)reaches 70-80%; 3)cane yields increase most significantly with soil water, but the increases of the two treatments at the WHC’S of 70-80% and 90-100% do not show significant difference; 4)sugar content decreases significantly if water deficiency occurs seriously at FGS, in spite of normal soil poisture at MSP.The tests at MSP show that 1)sugar content decreases most significantly with the increase of WHC(the former decreases by 0.32-0.5% as the latter increases at 10%); 2)the increase of WHC has no marked effect on cane yields; 3)the WHC’S of 30-40% are adequate.The physiological indexes of water at FGS tests indicate that irrigation is necessary as the intake force of cane leaves is above the critical level of 11.5 bar.