Vertical engineered barriers are often used to prevent the transport of heavy metal ions in groundwater, and barrier layers are the key to pollution control. In this study, modified calcium-based bentonite (CB) was prepared via the modification of CB with sodium carboxymethyl cellulose (CMC) and sodium hexametaphosphate (SHMP) for the prevention of heavy metal ions transport. CMC-SHMP@CB composites were prepared by pulping, drying and grinding. Structural characterization was performed by using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The swelling, permeability and adsorption properties of the CMC-SHMP@CB composites were further evaluated. The results show that these CMC-SHMP@CB composites have a hybrid microstructure from the intercalation and exfoliation action during modification. The swell index in deionized water of the CMC-SHMP@CB composites is 24.4 mL/2 g, which is 4.8 times that of the original CB index. Modification of CB with CMC and SHMP significantly improves its anti-permeation performance. In the presence of Cd2+ and Ni2+ ions, the hydraulic conductivity of the CMC-SHMP@CB composites still reaches ~ 3 × 10-11 m/s, which is much lower than the value of untreated CB. The adsorption capacity values of CMC-SHMP@CB for Ni2+ and Cd2+ were 11.01 mg/g and 13.82 mg/g, which are 5.6 times and 7.2 times the values before modification. CMC-SHMP@CB composites have great potential for use as the barrier layers for the prevention of heavy metal ions transport in groundwater.