In this paper, a micromechanical approach is developed to predict crack opening displacement (COD) of fiber-reinforced ceramic-matrix composites (CMCs) under tensile loading considering matrix fragmentation. The shear-lag model is adopted to obtain the micro stress filed of the damaged CMCs with matrix fragmentation and fiber/matrix interface debonding. The CODs of three different types of matrix fragmentation lengths, i.e., long, medium, and short fragmentation, are obtained considering relative slip between the fiber and the matrix. Relationships between composite constituent properties, COD, and matrix fragmentation are established. Effects of composite constituent properties (i.e., fiber volume fraction, fiber radius, and fiber and matrix Young’s modulus), matrix fragmentation length, and interfacial shear stress on crack opening displacement (COD), crack opening stress (COS), interface debonding ratio (IDR), interface complete debonding stress (ICDS), and axial fiber and matrix displacements (AFD/AMD) at the crack plane are analyzed. Experimental COD, COS, ICDS, IDR, AFD, and AMD at the crack plane of Hi-Nicalon™ SiC/SiC minicomposite are predicted for different matrix fragmentation lengths. The COD increased with applied stress, and can be divided into two regions corresponding to the interface partial and complete debonding, and the increasing rate of COD in the partial interface debonding region was much higher than that in the complete interface debonding region. When the matrix fragmentation length increased, the difference of COD was very small in the interface partial debonding region, however, in the interface complete debonding region, the COD increased with matrix fragmentation length, the COS, ICDS, AFD, and AMD increased.