Freeze-thaw action is a common geologic hazard factor for engineering foundations in mid and high latitudes. The strength evolution of silt soil subgrade modified by cement-asphalt powder under freeze-thaw cycles and its macro-micro mechanism were investigated using unconfined compressive strength test, nuclear magnetic resonance test and electron microscope scanning. The results showed that the unconfined compressive strength of stabilized silt soil with different asphalt powder dosages tended to decrease with the increase in the number of freeze-thaw cycles. However, increasing the asphalt powder dosage can significantly reduce the rate of strength deterioration. When the dosage of cement and asphalt powder is 6% and 4% of the dry weight of the silt soil respectively, the 28-day strength of the stabilized silt soil is 2.11 MPa, the rate of strength reduction after 12 freeze-thaw cycles is only 35.0%, the freeze-thaw resistance of the stabilized silt soil is optimal, resulting in the highest overall economic benefits and engineering performance. Under the action of the freeze-thaw cycle, the change in the internal pore structure and particle association mode of the stabilized silt soil are important reasons for the reduction in its strength. As the number of freeze-thaw cycles increases, the internal small pores of the soil body are transformed into medium and large pores. At the same time, freezing and thawing cause the gel material between the soil particles to fall off, reducing the strength of the intergranular bond and changing the soil structure from dense to loose. Macroscopically, the soil body on the surface of the sample is detached and the strength is reduced.