The radon control mechanism of Na₂O·nSiO₂−CaCl₂ modified soil was studied through the laboratory simulation experiment of tailing covering radon control. The radon exhalation rate (J) is negatively correlated with the coverage thickness (H), and it has a non-linear relationship with the temperature. The moisture content variation rate of the covering soil significantly decreases, which helps to reduce soil damage and enhance the resistance of the covering soil to ambient temperature interference. The formation of silicic gel and C−S−H gel effectively optimizes the pore structure and permeability, reduces the diffusion and migration of radon gas in the covering soil, and the average radon exhalation rate is decreased by 1.01×10⁻² Bq/(m³·s). The research results show that the Na₂O·nSiO₂−CaCl₂ modified covering soil can effectively improve the radon control performance of the covering soil and reduce the cost of cover treatment.