Abstract: Water infiltration, migration, and phase change of temperature are the crucial causes of frost damage in soils in cold regions. Modifying the soils to impart hydrophobic properties can effectively enhance their water resistance, offering a new approach to improving the frost and seepage resistance of the soils in these regions. The representative silty clay from Qinghai, a typical cold region, is selected, and the soil samples with varying compaction degrees and contents of hydrophobic agent using a novel hydrophobic agent are prepared. Through a series of contact angle tests and breakthrough pressure experiments, the effects of the compaction degree and the content of hydrophobic agent on the water repellency and breakthrough pressure of the soil samples are investigated. The results indicate that the water repellency of the modified Qinghai silty clay approaches superhydrophobic levels. Increasing the compaction degree and optimizing the content of hydrophobic agent significantly improves the contact angle and breakthrough pressure of the soils. There is a positive correlation between the breakthrough pressure and the compaction degree, and the breakthrough pressure exhibits a unimodal distribution with varying contents of hydrophobic agent. Under the conditions of a compaction degree of 0.95 and a content of hydrophobic agent of 13.0%, the hydrophobic soil exhibits 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.