Abstarct: The cost of energy for electric power generation, raise the level of productivity of the electric grid sectors. The interest in using solar energy to provide electricity visible programs. Improve voltage stability and thus increase the load on the distribution networks before the voltage collapse, as one of the most important criteria for determining the level of penetration of distributed generation (DG) in the electricity distribution network. Power distribution system characteristics, such as relatively high R/X lines and the widespread presence of solar photovoltaic (PV) as one of the most important sources of renewable energy, extensive studies to investigate the issues and take effective distribution networks. The events that have led to the collapse of the power grid voltage, we will assure the stability of the grid voltage to the widespread use of its resources. In this thesis, the analysis of voltage stability and power losses in distribution networks with the PV and the methods used to check the voltage stability. First of a voltage stability index and the curve of the voltage-power, PV effect on the stability of the losses in the distribution system is analyzed. In this thesis a practical solution for voltage stability analysis with the definition provided for PV penetration and of the power distribution system is implemented IEEE 34 nodes test feeder. The simulation results show that the method presented in this thesis has been baxsed on the characteristics mentioned in the analysis of voltage stability and losses, show the effect of PV penetration.