In Wenchuan Earthquake, masonry-infilled frames have the quite critical failures. In this paper, the reason of the failure phenomenon is analyzed and the influence of the infilled wall to performance of the frame is highlighted. An improved three-strut model for masonry-infilled frame structures is presented. Then, two RC frame specimens, which are modeled by the presented three-strut model and force-based beam-column element combined with fiber section considering compression-bending coupling in Opensees, are analyzed. The analytical results agree well with the experimental results. It is shown that the presented three-strut model is sufficient to simulate the performance of the infilled wall.