Abstract: In order to provide reliable reference for the design of strengthened storey in high-rise buildings, this paper presents a reduction coefficient equation of the horizontal top deflection based on a simplified outrig- ger model.The virtual work principle as well as the deformation compatibility conditions between outriggers and core wall are also considered.The influencing factors of the restraining moments of outriggers and reduc- tion coefficient of the horizontal top deflection such as the core-to-column rigidities α,core-to-outrigger rigidi- ties β and variation of cross-section of frame-core are analyzed.Some conclusions and case study are presented to be as reference for the strengthened storey design of high-rise buildings structures.