Abstract: In this report we suggest to use an improved tri-linear loop restoring force model. From the stand point of the relation between concrete slrcss and strain, a computer calculating method on the restoring forre skeleton curve of flexed destructed beams and columns is established, and a simplified calculating formula on restoring force characleries parameter, is presented. In comparing the calculating results with the actual test results, the reliability of the calculating method put forward by us in this report, is being proved.