Abstract: As for the distribution law and influencing factors of longitudinal temperature field in tunnels in cold re? gions, an indoor model test device is developed to analyze the effects of tunnel length, temperature and air velocity at the tunnel portal on distribution of longitudinal temperature field in tunnels in cold regions. The results show that the influence of tunnel length on longitudinal length under negative temperature is smaller when the air velocity at the tunnel portal is smaller and the temperature at the portal is higher; the longitudinal length under negative temperature in the tunnel increases linearly as a function of tunnel length when the air velocity at the tunnel portal exceeds a certain critical value and the temperature at the portal is lower than a certain critical value; the influence of the temperature at the portal on the longitudinal length under negative temperature in the tunnel is smaller when the air velocity the tunnel portal is higher and the tunnel length is shorter; under a certain air velocity at the tunnel portal, the longitudinal length under negative temperature in the tunnel increases linearly along with the decrease of the temperature at the portal when the tunnel length is long enough. The relationship between the longitudinal antifreezing fortification length and the air velocity at the portal follows a power function. The influences of temperature and air velocity at the portal on temperature field in tunnels in cold regions are promoted and strengthened with each other. The order of sensitivity of each factor to the longitudinal temperature field in tunnels in cold regions is: air velocity at the portal > air temperature at the portal > tunnel length. For a specific tunnel in cold regions, various factors should be comprehensively considered, and specific analysis should be made in terms of the anti-freezing design.