Abstract: The breakage micro-mechanism of plain-woven fiber reinforced composite materials was studied by meansof t ransverse compressive and tensile experiment s. It is observed that the shear damage along 45°with the fill st randoccurs together with interlaminar cracks during the process of t ransverse compression. The damage forms of warpst rand and fill st rand are different because of the curve diversity , and the st rand interfaces and laminar interfaces atf ree-edges show different shear failures. The differences among failure models are due to the different bendingshapes of st rands. These phenomena were analysed through microscope observation and numerical simulation. Somepossible reasons were given to explain these failure forms. The main reason may be that the interlaminar shear st ressis induced by highly anomalous st rand st ructure under t ransverse compression.