In order to improve the performance of attapulgite (ATP) in remediating heavy metal contaminated soil, the composites of ATP-rice straw, containing ATP of 25% (F-25), 50% (F-50), 75% (F-75), 100% (F-100) and 125% (F-125) in rice straw, respectively, were prepared by anaerobic fermentation, the passivation rates of ATP-rice straw composites on cadmium (Cd) contaminated soil were studied. ATP-rice straw composites were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), and then the passivation mechanism was discussed. The results showed that the contents of exchangeable Cd, carbonate Cd and Fe/Mn oxide Cd in soil were reduced, while the content of residual Cd was increased under the condition of the composite materials. F-25 reduced the contents of exchangeable, carbonate and Fe/Mn oxide Cd by 14.11%, 5.95% and 10.66%, respectively, while residual Cd was increased by 29.15%. F-25 with 3% addition amount and F-50 with 5% addition amount had better passivation rate (59.88% and 62.50%, respectively). The passivation rate of composites was increased rapidly with passivation time, then increased slowly after 15 days. Considering the influence of ratio of ATP-rice straw composite, the addition amount of the composite and passivation time on passivation effect of soil Cd and their cost, the composite material F-25 is given priority and the addition amount of 3% is recommended in remediation of Cd-contaminated soil.