The present invention relates to an agricultural water-recycling system comprising an iron (Fe)-ionizing module and a method of recycling agricultural water using the same, and more particularly to an agricultural water-recycling system comprising an iron (Fe)-ionizing module and a method of recycling agricultural water using the same, in which phosphorus (P) contained in effluent from a sewage treatment plant is removed by using the iron (Fe)-ionizing module comprising an iron (Fe)-ionizing electrode consisting of an iron plate serving as a cathode and a titanium plate serving as an anode and an electrode-washing device. According to the present invention, an effluent treatment process of a sewage treatment plant and an electrode washing process needed for iron ionization can be simultaneously performed, the iron ionization is controlled depending on the concentration of phosphorus contained in the effluent, thereby improving effluent treatment efficiency.