Different devices are used for the purpose of controlling the voltage of the transmission network buses. The Static Var Compensators (SVCs) are examples of these devices which have fast response to the disturbances. Hence, the reactive power reserves of the SVCs should be retained in order to overcome the large disturbances. In addition, to reduce the failure rate of secondary voltage control devices such as capacitors and Load Tap Changers (LTCs) their switching and changes should be minimized. Accordingly, the importance of the coordinated control of reactive power sources and voltage control has continued to grow rapidly due to the restructuring of the distribution system which leads to the mid-term planning of the reactive power sources and fast changes in the active and reactive power load profile In this thesis, a coordinated voltage control scheme is proposed based on a defined optimization problem, which simultaneously improves the performance of the transmission system operational indices, reduces the switching of the capacitors and the changes in the LTC taps, and increases the reactive power reserve of SVC. This multi-objective problem is solved using three methods consists of defining fuzzy membership for different target functions, multi-objective problem transformation into a single-objective problem using appropriate weights, and solved augment Epsilon constraint method, also, the obtained solutions are compared under different scenarios and conditions. In addition, the performance of proposed control scheme has been evaluated for different load profiles due to the increasing the penetration of photovoltaic sources in the distribution systems and the cases of utilizing voltage control algorithms which are based on active and reactive power management. The results show the impressive performance of the proposed method which suggests the implementation of reactive power sources for the purpose of voltage control. Moreover, a network voltage sensitivity model is proposed to control the voltage control devices and based on this, the network's linear relationships are used in the coordinated voltage control scheme. In this way, the time of the optimization problem solving and the decision control variables are considerably reduced. The performance of the proposed methods has been verified on the IEEE 24 and 30 bus test system. and the optimization problems conducted in GAMS software. Keywords: 1- Coordinated voltage control, 2-Voltage Control devices, 3- linear network's model, 4- multi-objective problems 5-reactive power reserve of SVC