By studying the influence of the debonding fibers in composites under cyclical thermo mechanical load the distributions of fibers and matrixes stress are given around the debonding fiber. For illustrating the Boron/Al, continuous fiber composite is examined. Matrix around the debonding fiber only sustains shear stress. The constitution relationship of matrix is perfect elastical-plastical. The important conclusion is made, which lays a foundation for continuing studying the fatigue of composites.