To study multi-bolt composite joints, this paper develops a numerical method to simulate composite joints through detail mechanical analysis of the multi-bolt area, considering the bending effect between interface of the bolts and the laminate wall. The method is validated by comparing load-displacement characteristics to experimental results, which is proved to be more accurate than the traditional method in explaining the real mechanical characteristic of composite joints. And then, the method is used to study the effects of plate thickness on bending in composite joints. Finally, a program, using MSC.Patran secondary development language PCL, is developed to realize the numerical method more efficiently.