Abstarct: Reliability is a key parameter in assessing the performance and stability of the power system. So that for the normal operation of a network, the minimum allowable value is required. In assessing the reliability of systems, parameters such as the amount of spinning reserve in power generation, transmission and distribution in the ring network, voltage control and control of the mega-like network, etc. are involved. This means that today generates reactive power equipment in the power network is so important. Due to the stability of modern power systems, integrated and interconnected networks are utilized. On the other hand, for economic reasons, maximum utilization of light generation network is required, productive operation of the transmission lines are placed. This causes even more important in today's networks is the reactive power injection. Because Mqdaryaby correct placement and installation of equipment for producing reactive power in terms of both economic stability is essential for modern systems. In this thesis the reactive power and its various aspects are discussed and reliability of the power system to be fully defined. And the role of reactive power in power systems reliability evaluation is expressed. First, the definition and modeling of power system reliability evaluation indices are. These indicators are divided into two general groups of related indicators associated with reactive power and reactive power is divided. Jbransaz•hay also be reactive and effective role in improving the voltage profile, power dissipation and reliability indices are discussed. The continuing impact of the baxse voltage set point, the reactive power produced by the generator and exit lanes productive and less time on the increase and decrease reliability indices, voltage profile and power losses were evaluated. The results mentioned above, which was divided into 16 scenarios were analyzed and the results were compared.