Abstract: This study investigated the damage evolution of 3DN C/SiC under monotonic and cyclic tensile loading using acoustic emission (AE) monitoring combined with micro-computed tomography (Micro-CT) characterization. K-means clustering algorithm was employed to classify AE signals. Results reveal significant anisotropic pore distribution with overall porosity of 11.9% and pore sizes ranging from 60 to 245 mm; porosity fluctuates sinusoidally (3.4%-20.9%) along the needling direction while varying gently (8.5%-17.4%) in the lay-up plane. Optimal clustering numbers of K=6 for monotonic loading and K=5 for cyclic loading were identified based on Davies-Bouldin index and silhouette coefficient, distinguishing damage modes including interface debonding in needle fiber tow, transverse/longitudinal matrix cracking, interface sliding in longitudinal fiber tow, fiber breakage, and fiber tow breakage. Hysteresis loop analysis established the evolution of interface sliding stress (5.28→1.49 MPa) and interface debonding energy (0.66→6.82 J·m⁻²). A three-stage failure mechanism was revealed: initial interface debonding, crack arrest with fiber bridging, fiber fractures. The dual role of needle fiber tow as both crack initiation sites and delamination suppressors was clarified, providing experimental foundation for reliability design of 3DN C/SiC.