A micromechanical was established based on the microstructure and the fracture mechanism of TiC-TiB2 ceramic prepared by combustion synthesis under high gravity. Two different failure modes were assumed in the micromechanical model to analysis the influence of alumina inclusions to ceramic strength. The equivalent stiffness of TiC-TiB2 matrix was calculated using the Interaction Direct Derivative (IDD) estimate. The alumina particles were considered sparse distribution in the TiC-TiB2 equivalent matrix, stress field contained residual stress in and around alumina particle was obtained by the equivalent inclusion method. According to the stress field around the particles, Al2O3 particles failure was considered as the origin of the composite fracture. Interface debonding and particle fracture were assumed as the two failure modes of particle failure, micro strength mechanical models based on these two modes were established and the minimum strength was defined as the composite strength. Composite strength variation with microstructure parameters and property parameters of different micro components was obtained, and the calculated strength was compared to the experimental data. The result shows that the strength model is reasonable in reflecting the composites failure mechanism; relative elastic and thermal properties between the particle and matrix, particle size and the equivalent matrix toughness can change the particle failure mode, and the particle size increasing and the equivalent matrix toughness decreasing result in composite strength necessarily. For TiC-TiB2 combustion synthesis composite with alumina inclusions, particle interface debonding is the primary fracture mechanism.