Abstract: This paper aims to clarify the microstructure characteristics and damage mechanism of paleosol with different water contents under freeze-thaw cycles. It uses the nuclear magnetic resonance scanner to test the paleosol samples with different water contents after freeze-thaw cycles. It studies the combination of freeze-thaw cycles and water content on the microstructure of the paleosol and the internal damage changes of the soil. The results show that the different water contents under freeze-thaw cycles cause different degrees of damage to the interior of the soil. The damage degree is that the soil with high water content is greater than that with low water content. As the number of freeze-thaw cycles increases,the signal amplitude of the T₂ spectrum curve increases,the pore structure changes,the content of macropores and maximum pores increase,and the content of mesopores decreases. At the same time,the increase in pore volume of soils with larger water content is greater than that of soil with lower water content. These results show that the greater the water content in construction projects in seasonal frozen soil areas,the more likely the soil mass is to be destroyed. So the waterproof and drainage problems should be paid attention in the project. According to the principle of damage mechanics,the relationship between soil particle continuity and porosity is obtained. Then the relationship between effective stress and porosity is obtained. According to the results of nuclear magnetic resonance scanning,this paper establishes the relationship between porosity and the number of freeze-thaw cycles,and finally derives the expression of the relationship between the effective stress of the paleosol and the number of freeze-thaw cycles. The research results provide theoretical guidance for the construction projects of paleosol strata in seasonally frozen soil regions.