To study the evolution law of the mechanical properties of cement mortar under the influence of the relative ice content in pores, based on the resistivity test results of cement mortar under periodic temperature variations, the time-history variation law of the relative ice content of cement mortar was calculated and analyzed. Using the PPR modeling technology, a calculation model for the relative compressive strength under the influence of different relative ice contents was established. The results show that under periodic temperature variations, the resistivity of cement mortar has a strong correlation with the relative ice content, and the established calculation model can effectively predict the changes in relative compressive strength with changes in the water-to-binder ratio, saturation, number of cycles, and maximum relative ice content of cement mortar under periodic temperature variations.