A pot experiment and an incubation experiment were conducted to investigate effects of soil moisture content [percentage of water holding capacity (WHC)] on the fresh biomass of and Cd concentration in lettuce ( Lactuca sativa ), soil pH and Cd availability in soil. Results show that soil moisture affected significantly biomass of the plant. In Treatment 75%WHC, The plant was the highest in fresh biomass, and an inverse “V” shaped curve of relationship was observed between fresh biomass and soil moisture. Soil moisture also affected markedly Cd concentration in shoots and roots of lettuce, and what’s more, a significantly negative relationship was found between the former and the latter. When soil moisture was increased from 45%WHC to 65%WHC, Cd concentration in the shoots decreased by 41%, which means that the Cd concentration in the vegetable is lowered from the grade of higher-than-the-hazard-free- standard down to the grade of lower-than-the hazard-free-standard. Cd concentration was significantly higher in roots than in shoots in all the treatments except Treatments 55%WHC and 75%WHC through T test. It was also found in the pot experiment that concentration of NH₄OAc extractable Cd in the soil was insignificantly related with soil moisture and with Cd concentration in shoots of the plant, too. Besides, soil moisture did not have much effect on soil pH, either. But in the incubation experiment, concentration of NH₄OAc extractable Cd in soil was markedly correlated with soil moisture, showing a negative relationship. It is preliminarily assumed that the effect of soil moisture on Cd concentration in shoots is not rendered through its effect on pH and NH₄OAc extractable Cd concentration of the soil. Anyway, it is feasible to control Cd concentration in the edible part of leafy vegetables growing in greenhouses with soils slightly polluted with heavy metals by regulating soil moisture content, which is a green environment-friendly measure that enjoys broad prospect of application.