Abstract: Heavy metal pollution of greenhouse soils are of great concern. In order to find out the application effects of biochar on heavy metal Cd in greenhouse soil, three levels of biochar, B0 (0 t/ha), B10 (10 t/ha), B20 (20 t/ha), were designed. The effects of biochar on Cd bioavailability, fractions, and uptake of metals by lettuce plants in metal-contaminated greenhouse soils were studied. Results showed that the application of biochar increased soil pH and soil organic matter, and changed Cd fractions in the soil. There was a greater decrease in the exchangeable Cd fractions but an increase in the oxide- and organic-bound and residual fractions with the application of biochar. The rates of Cd immobilized in soil increased with the amount of biochar applied. The exchangeable Cd fractions in soils amended with B10 decreased by 45–62% and in soils amended with B20 by 66–89% compared with the control. In addition, the addition of biochar had better effect on Cd immobilization in the low heavy-metal-contaminated soils than in the high heavy-metal-contaminated soils. Therefore, the application of biochar could change Cd fraction of greenhouse soil, reducing the bioavailability of heavy metals in the soil, but had no effect when in heavily polluted Cd greenhouse soil.