An analytical methodology was developed to investigate the effect of fiber/matrix interface debonding on matrix multicracking evolution of fiber-reinforced CMCs(ceramic-matrix composites). The Budiansky-Hutchinson-Evans shear-lag model was adopted to analyse the micro-stress field of the damaged composites. The critical matrix strain energy criterion

which presupposes the existence of an ultimate or critical matrix strain energy with matrix

was obtained to simulate the matrix multicracking evolution of CMCs. With the increase of the applied stress

the matrix multicracking and fiber/matrix interface debonding occurred to dissipate the additional energy entered into the composites. The fiber/matrix interface debonded length under matrix multicracking evolution was obtained by treating the interface debonding as a particular crack propagation problem. The conditions for no-debonding and debonding during the evolution of matrix multicracking were discussed in terms of two interfacial properties

i.e.

the interface shear stress and interface debonded toughness. When the fiber/matrix interface was bonded

the matrix multicracking evolution was much more intense compared with the interface debonding; when the fiber/matrix interface was debonded

the matrix crack density increased with the increasing of interface shear stress and interface debonded energy. The theoretical results were compared with experimental data of unidirectional SiC/CAS(calcium alumina silicate)

SiC/CAS-Ⅱ and SiC/borosilicate composites.