Abstract: It has been demonstrated in previous studies that nitrite rubber toughened epoxy can increase the fracture tourghness of composites,but little has been done on the effect of various nitrite rubber additive proportions of matrix on other important mechanical properties of composites,such as interlaminar shear strength which proved fatal to laminate composites.Exprimental study is made to determine and compare the interlaminar shear,tensile,bending and vibration-damping properties of high modulus carbon/epoxy unidirectional composites with various contents of nitrite rubber(0,1000,15%,20%).Acoustic,emission(AE) technique is used to detect the formation and propagation of the damage zone in the composite specimens,The micro-structure failure modes of specimens are investigated by means of a scanning electron microscope(SEM).Comparison is made among the four types of specimens,and the optimal proportion,10%,of the nitrile rubber additive is determined.Based on these results,toughening and strengthening mechanism of the composite is discussed.