Abstract: The cohesive zone model (CZM) was employed to simulate the delamination and random crack initiation in composite joints. A bilinear cohesive law incorporating mode Ⅰ, Ⅱ and mixed mode was presented, which was validated by the simulation of double cantilever beam (DCB) test. Cohesive elements were inserted into the space between every two solid elements to predict the random crack initiation in the filler at the root of the composite joint. The composite joint was simulated under pull-off load, and the numerical result is in good agreement with experimental one. In addition, a series of simulation was carried out under different conditions, i. e. different strength of matrix and adhesive, different radius and different filler property. The numerical result shows that the strengths of matrix, adhesive and filler have great influence on the loading capability and the failure modes of the composite joint. The performance of the structure increases with increasing the filler radius.