To determine the long-term stability of cold region tunnel affected by climate warming, taking one tunnel as an example, the coupling model of the moisture-heatstress fields was built and the temperature field, stress field, and deformation field were all studied in 50 years. Based on these, the response surface method was used to calculate the reliability of tunnel engineering. The results indicate that the freeze-thaw ranges will be about 1.1 m 50 years later, which is twice as large as that in the initial stage of construction. Compressive stress of vault and tensile stress of tunnel floor increase with time, and floor heave will become during freeze-thaw. It is concluded that the long-stability of this tunnel can satisfy with the designing requirements using the designed structures and insulation measures. The reliability indexes decrease with time increasing, and the failure probability and reliability index respectively will be 5.69% and 1.9723 50 years later.