Abstract: Taking a cold-region tunnel as a case study, a coupled hydro-thermal-mechanical model was established to investigate the influence of water accumulation and frost heave at different locations on lining forces. The distribution characteristics and evolution patterns of the temperature field, freeze-thaw range, ice content, and lining stresses were analyzed under the condition of water accumulation and frost heave in the sidewalls. Based on this, the Monte Carlo method was employed to calculate and analyze the variation in tunnel reliability. The results indicate that: Frost heave due to water accumulation in the sidewalls has the most significant impact on tunnel stability. Both the minimum temperature in January and the maximum temperature in July exhibit an increasing trend over time, and the freeze-thaw zone of the surrounding rock gradually expands. The maximum stress in the lining structure shows a positive correlation with time, but its growth rate exhibits a negative correlation. The reliability probability of the tunnel gradually decreases over time, when the temperature increased by 2.6 ℃ and 4 ℃, the reliability of the tunnel decreased by 11.2% and 11.5% respectively under the condition of water accumulation and frost heave on the side walls compared to the uniform frost heave condition in 50 years.