The proportional method, based on the stress or displacement near the crack tip, is one of the most useful methods to easily obtain the accurate value of stress or displacement near the crack tip, is one of the most useful methods to easily obtain the accurate value of stress intensity factor. In this study, the method is applied to the analysis of stress intensity factor for an interface crack in bonded materials. In the interface crack problem, ratio of stress intensity between the treated problem and reference problem is not constant because of oscillatory stress singularity. However, relation between energy release rate K_i and distance r from crack tip becomes constant within the wide range of r/a. Then, the energy release rate can be easily calculated by using the proportional method.