Abstract: A shear type model is used as the dynamic analytical model for the whole structure and a semidegrading tetralinear model with a descending branch is selected as restoring force model for the interstory columns. The parameter of the restoring force model for the interstory force model is computed by the nonlinear relation of M-, and the corresponding program IDAFF is developed. By analyzing the difference of the result between IDAFF and TAT, it can be concluded that:the result on rotation of inter-story displacement complied with the codes is on the high side under a minor earthquake and is possible on the low side under a major earthquake.