Abstract: By analysis of the working principle of unbonded post-tensioned flat platecolumn and review over its calculation scheme under perpendicular load, a reasonable calculation scheme for unbonded post-tensioned flat plate-column structures under horizontal load is established. The inconsistency between stress calculation and displacement calculation for equivalent-frame under horizontal load is overcome, and the calculation methods for this kind of structure under perpendicular and horizontal load are unified. This paper provides a good principle for reasonable structural design.