We carried out a hydroponic experiment to study the effects of silicon (Si) on the growth, Cd content, nutrient absorption, photosynthetic characteristics and antioxidant enzymes activities of two cabbage (Brassica oleracea L.) cultivars with different Cdtolerancers (Cdtolerant ‘Niuxin’ and Cdsensitive ‘Lüfeng’) under Cd stress in order to reveal the alleviation mechanism of exogenous Si in cabbage under Cd stress. The results showed that: (1) Under the stress of Cd, the growth, contents of nutrients (Mg, Fe, Mn, Cu), the activities of antioxidant enzymes (SOD, CAT, APX) and photosynthesis efficiency of leaves in plants were decreased significantly, while the malondialdehyde (MDA) content in leaves and roots of cabbages were increased significantly compared with the control. (2) Supply of exogenous Si under Cd stress promoted the biomass of plants, raised the nutrition element contents in shoots and increased the photosynthetic parameters (P_n, G_s, T_r), fluorescence parameters (F_v/F_m, Φ_PSⅡ, qP) and photosynthetic pigment contents. At the same time, MDA contents in plants and the transportation of Cd from roots to shoots were reduced significantly. It is suggested that Si can alleviate toxic effects of Cd by reducing the accumulation of Cd in shoots, increasing the activities of antioxidant enzymes to reduce membrane lipid peroxidation, promoting nutrient absorption and transportation, and enhancing photosynthesis.