Abstract: The tunnels in seasonal frozen soil always suffer freeze injury and their structures and operation safety are often adversely impacted. To solve this problem, the thermal insulation design suitable for small-section tunnels of oil and gas pipelines in cold regions was proposed based on the meteorological characteristics of cold regions and the characteristics inside pipeline tunnels, e.g. perennial constant temperature in tunnel, perennial closed portal and small section. After the whole temperature field covering the pipeline and the rocks around the tunnel was simulated and analyzed, the location and length of the thermal-insulation layer were defined according to the temperature and the freezing and thawing situations of the rocks around the tunnel. A formula for calculating the reasonable thickness of the thermal-insulation layer for small-section tunnels of oil and gas pipelines in cold regions was established. And an anti-freezing scheme combining thermal-insulation layers and thermal-insulation doors was adopted. The thermal insulation design is applicable to small-section mountain tunnels of oil and gas pipelines in cold regions, and it can be also used as the guidance for pipeline tunnels with large section.