Damage to insulation layer of buried oil pipelines will significantly change the distribution of the soil temperature field around the pipeline, thereby affecting the thermal performance and operational safety of the pipeline. Based on the theory of multi?physics field coupling, this study establishes a three?dimensional steady?state heat transfer model to quantitatively analyze the temperature drop characteristics of the pipeline and the evolution law of the soil temperature field under different soil types (clay, loam, sand). The model was solved using ANSYS Fluent 2022, with the effect of moisture intrusion considered. The numerical simulation results show that in sand soil, the critical number of segments with complete insulation damage is 15 segments (each 100 meters), corresponding to a critical damage distance of 1.5 kilometers. According to this critical distance, initial monitoring points are set, and a total of 56 monitoring points are required for an 80?kilometer pipeline. The temperature at each monitoring point shows a non?linear decreasing trend along the pipeline. The outlet temperature at the 28th monitoring point (42 kilometers away) drops to the wax precipitation point of 45 ℃ for the first time. The "critical distance segmented monitoring method" proposed in this study can achieve accurate monitoring of the pipeline damage status in the sand soil section, providing technical support for the safe operation of the pipeline.