To study the influence of train speed on thermal insulation and anti-thawing measures for surrounding rock of tunnels in cold regions, it is necessary to analyze the temperature field. By using the Kunlun Mountain Tunnel Project in cold regions as a case study, the effects of external atmospheric temperature, piston wind effects caused by varying train speeds, and the driving resistance on the distribution of the tunnel’s internal temperature field were considered. A three-dimensional numerical calculation model including the surrounding rock, concrete lining, and tunnel air was established by utilizing the thermo-fluid-structure interaction (TFSI) technique. The thermal environment variations caused by trains at different speeds were predicted. The result shows that during long-term train operation through the tunnel, both the piston wind speed and the pressure difference between the front and rear of the train increase as the train speed rises. This, along with increased driving resistance, significantly raises the surrounding rock temperature. Regardless of operational duration, the radial temperature impact depth of the surrounding rock decreases with greater tunnel depth, and axial temperature variations are reduced. For long-term train operation at speeds of 80 km/h and 160 km/h, it is recommended to set the thermal insulation and anti-thawing lengths at the two tunnel portals of the Kunlun Mountain Tunnel to 420 m and 790 m, respectively, so as to effectively prevent thaw settlement hazards in the surrounding rock of the Kunlun Mountain Tunnel.