Preserving capacity of fast voltage controllers, such as static var compensators (SVC) is necessary for response to contingency. However, this controllers are first equipment which response to the voltage deviation. Hence, capacity of this equipment are used and capacity of secondary voltage control equipment, such as capacitor banks and LTCs remains unused. Therefore, implementing a coordinated voltage control system is necessary so that depending on the system load, voltage control is divide between primary and secondary equipment, and sufficient capacity for fast response of primary voltage control equipment is provided. The other challenge is the number of switching in capacitor banks and LTCs, which influence failure rate, reliability, and lifetime. The purpose of this thesis is to design a voltage control system, not only to implement the full capacity of the SVC, but also to result in the least switching in capacitor banks and LTCs. It also provides proper operation of system based on energy loss and deviation of bus voltages fromthe nominal value, especially in buses with sensitive loads. The proposed coordinated master plan voltage control consists of two stages. In the first stage, the optimal settings of voltage control system equipment for the next 24 hours are obtained by solving an optimization problem which consists of six objective functions.Two objective functions are related to SVC capacity usage, two objective functions are related to capacitor banks and LTCs switching, and two objective functions are related to system performance indices. In the second stage, the main objectives of the coordinated voltage control, namely the preservation of SVC reactive power reserve and maintainingthe voltage at buses that voltage control equipment are connected to them are provide by an online algorithm. When real-time system and predicted loads are different, or contingencies such as, outage of capacitor banks, LTCs and line occur, theproposed algorithm satisfies the desired objectives. Based on the level of system intelligence, communication platforms, and software programs requirements, two online coordinated voltage control algorithms are proposed. The first algorithm is based on the communication, hardware, and software facilities which exist in the conventional systems and the second one is based on the multi-agent systems in the context of smart grid. The performance of different parts of the proposed coordinated master plan voltage control is illustrated for IEEE 30-bus system.The developed scenarios are changing the number of SVCs, changing the SVC’s modes, presence or absence of LTCs, changing the load profile, various contingencies, and different objective functions. Keywords: 1- Static Var Compensator , 2- Secondary Voltage Control, 3- Multi-Agent System,4- Coordinated Control.