Because of human need for energy, extra special attention is in the usage of renewable-energy sources in recent years. On the other hand, environmental pollution is created with fossil energy. Photovoltaic (PV) energy is also one of the renewable-energy sources that are available in almost all parts of the globe, especially in Iran. One application of this energy is in water pumping system. In this paper, we precede the technical and financial study on photovoltaic water pumping system for irrigation of GORGAN's farm fields (one of Northern Province of Iran) with the RETScreen software tools. In order to the results, it is obvious that the usage of this clean energy causes the reduction on production costs during of its operation.