Buckling is the major mesoscopic deformation mechanism of the Mesozoic East Sichuan fold belt, which responsible for the approximately spaced pattern of folds, the long, stable extent of folds, and underdevelopment of regional thrusts in the fold belt. This paper uses FLAC6.0 software to simulate the formation of the fold belt for a variable detached basement thickness (DBT). No matter how the DBT is set, only trough-like folds form in the shallow cover, or the fold surface of the top layers of the Triassic strata. This suggests that the difference in depth of the detachment zone (DZ) throughout the belt: the DZ seems to occur in the cover in the area of ridge-like folds and in the basement in the area of trough-like folds. With the increase of the DBT, ridge-like folds are gradually replaced by trough-like folds in the deep cover, or the fold surface of the bottom layers of the Silurian strata. For a DBT value of 3-4 km, the simulated folds in the deep cover resemble those observed in the area of trough-like folds. When the DZ occurs in the Silurian strata, the simulated folds in the shallow cover have a similar geometry to those in the area of ridge-like folds. These inferences are confirmed in the interpreted seismic reflection profiles across the fold belt.