Abstract: This paper aims to investigate the strength degradation characteristic and microscopic mechanism of silty mudstone under freeze-thaw cycles. It carries out the uniaxial compression tests and the mercury intrusion tests on silty mudstone samples under different freeze-thaw cycles. After the uniaxial compression test, the fracture of the rock sample is scanned by SEM. The influence of the number of freeze-thaw cycles on the strength characteristics, failure mode and porosity of the silty mudstone is obtained. The mechanism of strength deterioration of silty mudstone under freeze-thaw cycles is discussed in depth. The research results show the follows. (1)With the number of freeze-thaw cycles increases, the uniaxial compressive strength and elastic modulus of silty mudstone decrease. The decay rate of uniaxial compressive strength keeps decreasing. The strain increases continuously when the rock sample fails. The decay rate of elastic modulus increases. The failure form of silty mudstone changes from brittleness to plasticity. (2)With the increase of the number of freeze-thaw cycles, the macroporous porosity, the mesoporous porosity and the total porosity increase exponentially, and the increase in mesopores is dominated. With the freeze-thaw cycle continues, some of the micropores are transformed into mesopores, and the porosity of the micropores increases at first and then decreases. (3)The mechanism of the decrease in uniaxial compressive strength and elastic modulus of silty mudstone under freeze-thaw cycles is as follows. The alternating water-ice phase increases the internal porosity of the rock mass, some of the micropores are connected and transformed into mesopores, resulting in an increase mesoporous porosity. It can be observed that for the silty mudstone under the freeze-thaw cycle, the increase in mesoporous porosity is the most important factor leading to the deterioration of its strength.