Abstract: Water infiltration, migration, and temperature phase changes are crucial causes of frost damage in soils in cold regions. Modifying soil to impart hydrophobic properties can effectively enhance its water resistance, offering a new approach to improving the frost and seepage resistance of soils in these regions. This study selected the representative silty clay from Qinghai, a typical cold region, and prepared soil samples with varying compaction degrees and hydrophobic agent contents using a novel hydrophobic agent. Through a series of contact angle tests and breakthrough pressure experiments, the effects of compaction degree and hydrophobic agent content on the water repellency and breakthrough pressure of the soil samples were investigated. The results indicated that the water repellency of the modified Qinghai silty clay approached superhydrophobic levels. Increasing the compaction degree and optimizing the hydrophobic agent content significantly improved the contact angle and breakthrough pressure of the soil. There was a positive correlation between breakthrough pressure and compaction degree, and the breakthrough pressure exhibited a unimodal distribution with varying hydrophobic agent content. Under the conditions of a compaction degree of 0.95 and a hydrophobic agent content of 13.0%, the hydrophobic soil exhibited the highest breakthrough pressure, reaching approximately 50 kPa. This study provides new experimental evidence for the design of seepage-resistant soils in cold regions and offers a reference for the future application of hydrophobic soils in cold region engineering.