Recently integral large composite structures have been applied to many structures of vehicles because of their low cost and high reliability. Since the structures are large and complicated, a damage estimation system is required to assess the safety of inspected damage. Among fracture mechanisms of FRP laminates, delamination is the most important one because it results in stiffness degradation of the structures. In this study, a simple estimation method of delamination growth for FEM using two-dimensional plane stress elements was proposed by using energy release rate, and inexpensive FEM simulation method for delamination growth was developed. To assess the safety of inspected damage, prediction of delamination growth and stiffness degradation are more important than that of fracture strength. Analytical results of delamination growth and stiffness degradation for a CF/epoxy laminate with an open hole were compared with experimental results. As a result, the simulation method was shown to be effective and inexpensive for predicting delamination growth and stiffness degradation.