In order to reveal the influence of the hydration heat generated by the secondary lining during high geotemperature tunnel construction on the service performance of the thermal insulation layer and further optimize the thickness of the insulation layer, the finite element numerical analysis method is used to study the heat transfer law of the insulation layer under the interaction of hydration heat and high rock temperature during the construction of the high geotemperature tunnel. The field measurement and numerical simulation is compared with the rock temperature change law behind the primary support to verify the rationality of the model. On this basis, the comprehensive influence of the thickness of the insulation layer and the convective heat transfer coefficient on the temperature field of the secondary lining is discussed. The results indicate that: (1) After pouring the secondary lining, the main heat transfer of the insulation layer is divided into three stages. The thermal insulation layer is in a heated state on both sides, i.e. the heat in the rock mass and that of hydration transfer to the insulation layer at the same time, the heat of hydration flows from the secondary lining side through the thermal insulation layer to the primary support side, and the heat in the rock mass flows from the primary support side through the thermal insulation layer to the secondary lining side. (2) The temperature of the thermal insulation layer near the secondary lining increases first and then decreases, and reaches the peak value of nearly 57 ℃ in the second stage. The temperature of the heat insulation layer near the primary support increases to a stable value of about 58 ℃. (3) Due to the existence of the thermal insulation layer, it is difficult for the secondary lining to conduct hydration heat through the surrounding rock, and most of the heat can only be dissipated by convection heat transfer with the air in the tunnel. Moreover, the closer the part of the secondary lining to the thermal insulation layer, the later the temperature peak appears and the higher the peak. (4) The use of 9 cmthick insulation layer and ventilation equipment that can provide an additional 2 274.342 4 m3/min required air volume and can achieve a relatively good cooling effect.