In order to study the effectiveness of air curtain insulation technology at tunnel portal in cold regions, the principles of fluid mechanics, superposition principle, and Bessel characteristic function were adopted, and a theoretical system for the temperature field of air curtain at tunnel portal in cold regions was constructed. The feasibility of this insulation technology was verified through numerical simulation methods, and the insulation principles of this insulation technology were summarized. The results show that the theoretical calculation results are relatively close to the numerical calculation results, and tunnel freezing damage can be effectively prevented by air curtain insulation technology. The insulation principle of air curtain insulation technology can be summarized as heating is primary and air isolation is secondary. The research results can provide a theoretical basis for future engineering practice.