In stress corrosion cracking, many surface cracks are initiated and the interaction between the cracks affects on crack growth behavior. Therefore, influence of the interaction on crack growth has to be taken into account in fitness-for-service evaluation. However, quantitative evaluation of magnitude of the interaction is difficult because many factors, such as the relative position, size and geometry, have influences on the stress intensity factor (SIF), which is driving force of the crack growth. In this study, in order to investigate the intensity of interaction, the SIF of interacting two semi-elliptical surface cracks was evaluated by the finite element method and finite element alternating method. These methods enable us to evaluate the SIF of interacting cracks for various conditions. The analyses were preformed under uniform tensile and bending load for various aspect ratios and relative crack sizes condition. The analysis results reveal that the change in the averaged SIF along the crack front caused by coalescence of two cracks can be estimated from the change in the area size. The maximum interaction can be estimated by simple addition of the area size of two cracks regardless of the loading condition and relative crack size. This was confirmed by the growth simulation of interacting cracks according to the power law of SIF.