Ceramic-matrix composites (CMCs) possess high specific strength and modulus at elevated temperature and have already been applied in hot-section components in commercial or military gas turbine engines. Due to low fracture strain in the brittle SiC ceramic, matrix microcracking occurs below the proportional limit stress (PLS). At elevated temperature, the opening of matrix microcracking affects the mechanical properties of CMCs when the oxygen or oxidative gas ingresses the composite through these cracks. To ensure the reliability, safety, and airworthiness level of CMCs components, it is necessary to understand the crack opening behavior of CMCs at elevated temperature. In this paper, a micromechanical approach is developed to predict the time-dependent crack opening behavior in SiC/SiC composite. Micro stress field in the different damage regions are obtained and the cracking opening displacement (COD) are calculated. Experimental CODs in SiC/SiC composite for different matrix crack lengths are predicted. Effects of composite material properties, stress level, and testing temperature on the time-dependent crack opening behavior in SiC/SiC composite are analyzed. Relationships between the cracking opening, composite’s constituent properties, stress level, and testing temperature are established. The analysis results can help the engineering designer better understanding the crack opening behavior in CMCs.