To ensure the safety and stability of the beach surface of the decommissioned uranium mill tailings pond, this paper uses red clay-bentonite and red clay (1:1) to carry out covering layer radon reduction simulation experiments to study the temperature, humidity, and radon reduction effect of the covering layer under natural conditions. The results show that the radon exhalation rate of red clay-bentonite cover layer is only 0.32 times that of red clay, which has a better radon reduction effect. The red clay-bentonite cover layer has better water retention and comparable heat preservation effect than red clay cover layer. The red clay-bentonite and red clay temperature curves follow the same evolution trend and were close together in the same outdoor conditions, and the humidity curves showed a difference of 1% to 3%. Soil temperature is the dominant factor affecting the variation of radon exhalation of red clay-bentonite and red clay covering layer with unsaturated water content.