During the operation of high-speed trains, due to the impact of different degrees of foreign bodies on the bottom plate of the equipment cabin under the train, the decline in the performance of composite materials affects the safety of train operation. Therefore, it is particularly important to find a reliable and accurate method to detect the damage location. Due to the change of structural parameters and modal characteristics of composite materials, a modal analysis method is proposed to predict the stress position of composite materials, and the relationship between modal parameters ( natural frequency and relative amplitude ratio ) and stress position is studied. The plane model of the composite was established by the modal analysis software m+p SO Analyzer, and the vibration characteristics of the composite were tested and analyzed. The contour maps of the natural frequency and relative amplitude ratio of the composite under different positions were established. Furthermore, the distance from the stress position to the center of the composite material is determined by the natural frequency ; finally, the stress position of the composite was determined by combining the relative amplitude ratio. The results show that the force position of carbon fiber epoxy resin composite specimen can be successfully predicted based on the change of natural frequency and amplitude, and the error can be controlled within 5 %.