Abstract: In order to solve the damage index of roadbed caused by rain exchange, by simulating the influence of water vapor exchange on highway subgrade in the climate area with frequent rainfall, the influence of drying-wetting cycles on modified soil of highway subgrade in northern Hebei was studied by indoor mechanical test. The results showed that the California Bearing Ratio（CBR） value and springback modulus of cement-modified soil at 28 days of curing met the exponential function relationship after the drying-wetting cycles. The dry-wet damage of cement-modified soil at 90 days of curing was the most obvious, followed by 28 days, and the early cement hydration can repair the damage caused by the drying-wetting cycles. Through microscopic comparison, it can be concluded that the skeleton area of modified soil samples with 28 d curing age increased first and then decreased with the increase of the number of drying-wetting cycles, and the skeleton arrangement also changed. According to the results of this study, it was recommended that the CBR（California Bearing Ratio） value of 7 d curing age should be 370% and that of 28 d curing age should be 500% as reference. Based on the unconfined compressive strength, springback modulus and CBR indexes, it was suggested that 6% cement content should be used as a reference for roadbed improvement in areas with frequent water vapor exchange.