Micromechanical damage of fiber/matrix interface under cyclic loading is simulated. The effects of loading conditions and shear deformation of matrix on interfacial debonding are considered and discussed. It is found that: (1) the force of interfacial fraction plays an important role in resisting interfacial debonding; (2) no matter what kind of the commonly considered loading conditions is, interfacial debonding always undergoes three stages though the damage degree is not the same; (3) the shear deformation of matrix has the ability to slow down the interfacial debonding rate.