Abstract: In response to the demand for heavy metal pollution barrier engineering in seasonal frozen soil areas, the effects of guar gum proportion and water bath temperature on the swelling index of bentonite were investigated. With cement as the base material, the effects of modified bentonite dosage, coal gasification slag (CGS) dosage, curing time, and freeze-thaw cycles on the impermeability and freeze-thaw resistance of the material were examined. The results showed that the optimal proportion of guar gum-modified bentonite was approximately 0.01%. Beyond this critical proportion, the solution became too viscous, leading to insufficient contact between bentonite and the polymer solution. The optimal modification temperature was 70 ℃, at which bentonite was fully hydrated and guar gum molecules maintained their optimal configuration with moderate system viscosity. The optimal mix ratio of cement-CGS-modified bentonite composite was 1∶0.56∶0.07. Compared with the optimal ratio of cement-modified bentonite (1∶0.07) cured for the same period, the permeability coefficient of the test block was reduced by 84.19%. The addition of CGS promoted pore filling and the formation of C—S—H gel. The permeability coefficient of the optimal ratio test block after 7 freeze-thaw cycles for 28 days of curing was 8.73×10⁻⁸ cm/s, demonstrating excellent freeze-thaw resistance. This research provides high-performance impermeable materials for pollution barrier engineering in seasonal frozen soil areas, offering significant theoretical and engineering application values.