In order to sure the favorable area of oil cracking gas in Sichuan Basin, the thermal evolution history of Sichuan Basin was reconstructed by geothermometer of vitrinite reflectance, and the distribution and evolution characteristic of favorable geothermal field for oil cracking gas reservoirs in Feixianguan Formation of Lower Triassic were determined. The results showed that the heat flow evolution after Triassic was inconsistent in different tectonic units in Sichuan Basin; and the differences were mainly caused by the uplift of Qinghai-Tibet Plateau and basalt mantle plume of Emei Mountains; the distribution of favorable geothermal field for oil cracking gas in Triassic Feixianguan Formation was ever changing; the distribution was almost over Sichuan Basin at the end of Jurassic, and reduced at the end of Cretaceous, and continually reduced to West Sichuan and part of Central Sichuan.