In order to explore the evolution law of temperature field after tunnel running through in cold area, taking Caomugou tunnel of Jilin-Tumen-Hunchun railway as the research object, according to the field temperature measured data, the equal proportion tunnel temperature field model is established by using ANSYS finite element software. Based on the heat conduction theory, the main factors affecting the evolution of temperature field are analyzed, and the control variable method is used to calculate the distribution law of longitudinal and radial temperature field of tunnel under different freezing periods, with or without train wind and different external temperature conditions. The results show that the measured section temperature of the tunnel is sinusoidal, and the farther away from the lining surface, the lower the temperature amplitude; During the freezing period of the whole tunnel, the temperature of only 280m is above 0 ℃, so cold proof and thermal insulation measures shall be taken for the whole tunnel; The freezing depth of tunnel portal section is closely related to the freezing time and external temperature. The longer the freezing time, the deeper the freezing depth. Under extreme temperature, the freezing depth of tunnel portal can reach 8.2m; Train wind speed has little influence on freezing depth, but the influence of train wind can not be ignored. The research results can provide theoretical data support for the frost damage regulation of Caomugou tunnel.