A greenhouse pot experiment with ryegrass was conducted to investigate the bioavailability of Cd in two simulated Cd-contaminated soils (yellow brown soil and red soil) and their components (colloids and de-colloid soils). EDTA effect on mobilization and bioavailability of Cd in the above growth substrates was also explored in this study. The results showed that: (1) the mean shoot height, shoot and root weight of ryegrass grown in different Cd-contaminated soils or their components were in the following decreasing order with colloid treatment> original soil treatment> de-colloid soil treatment. The total biomass of ryegrass grown in the Cd-contaminated colloid was 1.31±0.02 and 1.82±0.21 times higher than those in original soil and de-colloid soil, respectively. (2) Cd concentration and bioaccumulation factor in shoot and root were followed by colloid < raw soil < de-colloid soil, indicating the bioavailability of Cd in different soil components was colloid < raw soil < de-colloid soil. (3) the addition of EDTA into the original soils or their components led to significant increase of Cd concentration in shoot and root and the decrease of ryegrass biomass due to Cd phytotoxicity; and (4) Cd mobilization facilitated by EDTA was obvious especially in the yellow brown soil and two de-colloid soil components. It was concluded that Cd bioavailability was, to a great extent, affected by soil colloid quality and soil pH.