The dependence of toughening mechanisms on reinforcement orientation and the toughening effect governed by multiple toughening mechanisms were characterized for ceramic-matrix composites (CMCs) with discontinuous elongated reinforcements. Two kinds of Si3N4-based composites, with directionally oriented and randomly oriented SiC whiskers, respectively, were tested by the three-point bending of chevron-notched bars. Based on microscopic observations and micromechanical analyses, three mechanisms were confirmed to dominate the crack-bridging behavior: (1) bridging and breaking of long reinforcements, (2) frictional pullout and breaking of short reinforcements, and (3) local matrix spalling. Both the occurrence of the multiple mechanisms and their toughening effects were proved dependent on the reinforcement orientation. The combined effect of the multiple mechanisms correlated with random orientation thus was characterized by a statistical approach to solve for the crack-bridging stress function, The theoretical model was in good agreement with the experimental results.