Moraines are special rock and soil mass formed by the accumulation of large amounts of debris material transported by glacial action. Due to the geographical and climatic conditions prevailing, freeze-thaw action can pose a challenge to the construction of tunnels through this type of rock, especially in portal sections. The geological conditions of moraine surrounding rocks in Tibet, China, was investigated, and set up a direct shear test of freeze-thaw cycles to study the influence of the number of freeze-thaw cycles and water content on the mechanical properties and indicators of frozen moraine, introduced a comprehensive parameter K for the number of freeze-thaw cycles and water content, fit the formula for the cohesion c. The results show that the freeze-thaw cycles and water content have significant influence on the cohesion c. And proposed a formula for calculating the surrounding rock pressure applicable to the tunnel portal section of moraine surrounding rocks based on the Terzaghi theory. Taking a tunnel of Changlin Railway as an example, the surrounding rock pressure under different conditions was calculated to verify the reasonableness of the formula. The study shows that freeze-thaw cycles and water content are important factors affecting changes in the mechanical properties of moraines, and freeze-thaw action has different degrees of influence on the surrounding rock pressure in the portal section, which should be fully considered in the construction of the project.