Air temperature at northern high latitudes has increased at a higher rate than the global mean, and most general circulation models project that this pattern will continue. Climate warming can increase summer thaw depth and induce permafrost degradation, which may alter the dynamics and functions of northern ecosystems and the lifestyles of northern residents. To address these issues, we developed a process-based model to simulate permafrost thermal regimes by combining the strength of existing permafrost models and land surface process models. Soil temperature and active layer thickness were simulated by solving the heat conduction equation, with the upper boundary conditions being determined using the surface energy balance and the lower boundary conditions being defined as the geothermal flux. The model integrated the effects of climate, vegetation, ground features, and hydrological conditions on the basis of energy and water transfer in the soil-vegetation-atmosphere system. The model was validated against the measurements at four sites in Canada. The simulation results agreed with the measurements of energy fluxes, snow depth, soil temperature, and thaw depth. These results indicate that this physically based model captured the effects of climate, vegetation, and ground conditions on soil temperature and freezing/thawing dynamics, and the model is suitable to investigate the impacts of transient climate change on soil thermal regimes and permafrost degradation and their consequent effects on ecosystem dynamics.