Abstract: Infill walls are considered as non-structural elements，but they are still involved in seismic calculation． This paper considered the interaction between the main structures and fill walls，used OpenSEES to establish simplified model． Infill wall adopted improved equivalent slant strut based on FEMA model． Considering maximum drift as seismic demand parameter，incremental dynamic analysis was performed to obtain infilled RC frame's threshold values on target performance levels． Comparing the calculated results with pure framework and codes，it was indicated that the presence of infill walls could significantly improve lateral stiffness of frame structure and its seismic performance．