Foreland basins developed between fold-thrust belts and cratons which had been overthrusted by thrust faults. They were formed through regional isostatic adjustment and Theological flexure under the load of fold-thrust belts. This article discussed the internal relationship among lithospherical rheology, basin s forming and sedimentary filling under thrusting in the foreland area, and introduced two models of lithospherical rheological flexure during the development of foreland basins and the simulation of foreland basin-filing evolution.