Abstract: The Bouc-Wen model of an MR damper, the semi-active control law, and an elastic-plastic material model considering damage variables are developed through the secondary development of LS-DYNA program, which makes the refinement damage evolution simulation of a semi-active controlled structure in general finite element program come true. Based on the damage material model, two seismic performance indices for member and story level are proposed and also used to determine the maximal control force produced by MR dampers on different stories. As a numerical example, the damage control study on a 9-story benchmark steel frame are conducted, and the aseismic performance of the structure both with and without MR dampers are analyzed through IDA method. The results indicate that: damage accumulation effects of a controlled structure are obviously reduced by using optimally designed MR dampers, the damage distribution is more widespread, and the capacity of absorbing earthquake energy as well as the aseismic performance are all increased significantly.