Due to the lack of traditional paleothermal indicators/geothermometer, the evolution of basin thermal history and paleothermal field characteristics of the deep and ultra- deep carbonate formation in the western basin of China are controversial.Methods:Taking calcite in the Wufeng—Longmaxi Formation in southern Sichuan as an example, combined with fluid geochemistry and thermal evolution history, calcite mechanical twins can effectively reveal the thermal history characteristics of Wufeng—Longmaxi FormationResults:Calcite mechanical twins have three evolution processes: twins dislocation formation, twins thickening and merging of thickened lamellage , resulting in different twins structures (thin, tabular thick, curved and tapered etc.) formed in environments below 170℃, 170~200℃ and greater than 200℃, respectively, and with the increase of temperature, there are trend characteristics of decreasing twin density and increasing width. The Wufeng—Longmaxi Formation in Weiyuan area of southern Sichuan developed typical tabular thick calcite twins, with a width of 1~4 um and a density of 30~50 pieces/mm. The calcite twins of Changning Wufeng—Longmaxi Formation has a large width (about 3 um) and a low density (15~20 pieces/mm). The inclusion homogenization temperature and thermal evolution history showed that the peak of homogenization temperature in Changning was 120~140℃, 160~180℃ and 200~220℃, and their buried heat history was significantly greater than that in Weiyuan area, which together revealed that the Wufeng—Longmaxi Formation in Changning area had a higher temperature for mechanical twins formation compared with Weiyuan area.Conclusions:Calcite mechanical twins morphological geometry can be applied as a typical geothermometer to the study of the thermal history of deep carbonate formation in western China.