Abstarct: Optimal reactive power dispatchis one ofthe major issues in operation of power systems which aims to minimize losses, voltage stability, voltage deviation, etc. through an optimal adjustment of control variables. Recently, some alterations have been involved in control procedures, management and scheduling of these systems due to the power systems restructure, electricity markets and smart grids. These changes are not ablein method sused for optimal dispatch of reactive power as well. Accordingto the hierarchical structure of the powergrids, this thesis presents a hierarchica ldistributed frxamework baxsed on a System of Systems (SoS) concept. In this structure, every section ofthe gridis controlled by a smart agent. Agents are interconnected and exchange the required data via a telecommunication network. In this thesis, the amounts of active and reactive power exchanged between agents are consideredasboundary and common parameters.In this thesis, a SoS-baxsed control model is proposed to optimally distribute reactive power to smart grids. In this model, the power grid is divided into several domains at different levels in which monitoring and decision-making are carried out. The proposed method uses a mathematical approach to separate the power system into different parts. The proposed method is coded using GAMS software and implemented on a transmission system with 7 active power distribution networks. The results show that the proposed method in Comparison with centralized method and decentralized method has good performance in terms of computation time and fault tolerance compared to the other two methods.