In this study, debonded particles in a random participate composite are analyzed by three-dimensional finite element method to investigate their load carrying capacities, and the way to replace a debonded particle with an equivalent particle is examined. The variation in Young's modulus and Poisson's ratio of a damaged composite with the increase of the debonded angle was evaluated for different particle arrangements, which in turn compared with the results by equivalent inclusion method. Consequently, it was found that by replacing a debonded particle with an equivalent orthotropic particle, the macroscopic behavior of the damaged composite can be reproduced so long as the interaction between neighboring particles is negligible.