This paper presents the simple method to determine the complex stress intensity factor of interface crack problem by the finite element method. The proportional method is extended to the interface crack problem. In the present method, the stress values at the crack tip calculated by FEM are used and the stress intensity factors of interface crack are evaluated from the ratio of stress values between a given and a reference problems. A single interface crack in an infinite bi-material plate subjected to tension and shear is selected as the reference problem in this study. The accuracy of the present analysis is discussed through the results obtained by other methods. As the result, it is confirmed that the present method is useful for analyzing the interface crack problem.