Abstract: Yarns in the thin-walled plain woven composites are not homogeneous through the thickness, and hence there are noticeable discrepancies between the bending stiffnesses obtaied from engineering constants and the experimental results. A direct micromechanical method for predicting bending stiffnesses has been proposed here using the unit-cell finite element model. The path of the yarn center was taken to be periodic cubic bézier curve, and the 3D geometry model of a unit-cell was obtained assuming that the yarns enjoy constant cross section with a lenticular shape. The periodic boundary conditions for bending and twisting conditions were presented. Combing the cubic voxel mesh method, the non-uniform distributed displacement fields were applied by coupling the freedom degrees of the opposite points one by one. The tension, four-point bending and cantilever plate bending tests were conducted. The results indicate that the provided unit-cell finite element model can predict the bending stiffnesses precisely. As to the bending configuration of the cantilever plate, comparing with the results obtained from engineering constants, the results depending on the predicted stiffnesses agree better with the test.