Abstract:  Erlian Basin is one of the important petroliferous basins in China. Baibei Sag is one of the important petroliferous basins in Erlian Basin with exploration and development value. It develops many source rock intervals such as K₁t and K₁a. Exploring the tectonic thermal evolution history of Baibei Sag in Erlian basin is of great significance for the exploration and development of fossil energy in Baibei Sag. According to seismic and logging data, combined with temperature measurement data, the erosion thickness of K₁s and K₂e is restored by using mudstone acoustic time difference method and vitrinite reflectance method, and then the burial history and tectonic thermal evolution history of Baibei Sag in Erlian Basin since Cretaceous are restored. The results indicate that Baibei Sag in Erlian Basin exhibits structural development characteristics of "differential subsidence in the early stage, uniform subsidence on a large scale in the middle stage, and overall uplift and erosion in the late stage". By the end of the Early Cretaceous, the Arshan Formation reached a maximum burial depth of 3483m, and the first phase of uplift and erosion occurred towards the end of the Saihantala Formation's deposition, with an erosion depth of about 1314m. Influenced by the Himalayan movement during the late Cretaceous, the Erliandabusu Formation, with a thickness of about 408m, was deposited. Subsequently, a second uplift and erosion event occurred towards the end of deposition, resulting in an erosion depth of about 166m. Since the Paleogene period, the sag has been in a stable subsidence phase, characterized by a small sedimentary thickness and a tight deposit of 100m of Cenozoic strata. The current geothermal gradient in Baibei Sag stands at 2.94℃/100m, while the current geothermal flow value is 58.8mW/m². The average geothermal gradient during the maximum burial depth in the Early Cretaceous was 3.65℃/100m, indicating a thermal abnormal state. The source rocks of the Arshan Formation entered the mature stage at about 103Ma during the Early Cretaceous, while the source rocks of the Tengger Formation entered the low mature stage at around 105Ma during the same period. The source rocks in Baibei Sag reached their maximum thermal evolution degree at about 77Ma during the Late Cretaceous (Tengger Formation: 0.50%<Ro<0.68%; Arshan Formation: 0.72%<Ro<0.76%), indicating significant hydrocarbon generation potential.