Abstract: The incremental dynamic analysis (IDA) method is a good tool to evaluate the seismic performance of structures. However, it is computationally expensive to conduct inelastic dynamic analysis. In this study, a simplified incremental dynamic analysis method is proposed for the seismic evaluation of plan-asymmetric structures by introducing the equivalent dual degree of freedom (EDDOF) model into the process. With 20 ground motions and a 5-story plan-asymmetric frame structure, the incremental dynamic analysis is performed based on the original structures and the corresponding EDDOF system. The IDA curves and the collapse fragility curves are compared for the two methods. It can be concluded that the simplified IDA method is reliable and effective for evaluating the seismic performance of uniaxial plan-asymmetric structures from elastic behavior to global dynamic collapse. And the proposed procedure also has good efficiency.