Foreland thrust belts have shown great hydrocarbon potential and their oil and gas occurrences are controlled by the structural segmentations. Longmen Mountains thrust belt is characterized by the structural segmentation, but there is rarely research on the segmentation mechanism. The results of sandbox experiments have identified the basement difference and indenters in the thrust belt as the main controlling factors over the structural segmentation of foreland thrust belts. Recently research has presented the existence of Western Sichuan palaeo aulacogen in Sinian strata, associated with two large scale palaeo uplifts, including Dayi palaeo uplift and Jiangyou—Laoguanmiao palaeo uplift, which lead to basement difference in the basin. Combining with the geological condition of Longmen Mountains thrust belt, the structural segmentation mechanism of Longmen Mountains thrust belt can be concluded as follows：the northern segment formed firstly when the Bikou block transmitted power and was blocked by the margin palaeo uplift of Longmen Mountains initial rift inside the basin. Central segment corresponds to Western Sichuan palaeo aulacogen, where Pengxian—Guanxian（Dujiangyan）complex squashed into the basin and inheritably formed Western Sichuan foreland basin during Yanshanian—Himalayan Periods. Southern segment formed thrust belt above Dayi palaeo uplift when Baoxing complex transmitted power.