Prepreg properties including cure kinetics, cure shrinkage, and coefficient of thermal expansion were analyzed. A simulation method based on “element birth and death” method of Finite element analysis(FEA) was presented to simulate the cutting process and predict the machining deformation for composite laminates and stiffened panels. The comparisons between the simulation results and experimental data showed good agreement. It is found that residual stresses are the main source of machining deformation for composites and machining deformation is expected to happen only if there are stress gradients along the machining direction. There is no machining deformation for composite laminates due to its uniform stresses distribution in plane, while machining deformation can be observed obviously for T-shape stiffened composite panels. Attention should be paid to machining deformation to avoid the mismatch during assembly. A simulation method based on “element birth and death ” method of Finite element analysis (FEA) was presented to simulate the cutting process and predict the machining deformation for composite laminates and stiffened panels. The comparisons between the simulation results and experimental data showed good agreement. It is found that residual stresses are the main source of machining deformation for composites and machining deformation is expected to happen only if there are stress gradients along the There is no machining deformation for composite laminates due to its uniform stresses distribution in plane, while machining deformation can be seen obviously for T-shape stiffened composite panels. Attention should be paid to machining deformation to avoid the mismatch during assembly.