Secondary-treated municipal wastewater (MWW) is the alternative water source in recirculating cooling water systems. Municipal wastewater treatment plant (WWTP) effluent was collected and four fractions including hydrophobic acidic (HPOA), hydrophobic alkaline (HPOB), weakly hydrophobic (WHPO) and hydrophilic (HPI) organics were isolated from the effluent by using DAX-8/XAD-4 resin. We used potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) to investigate corrosion characteristics of N80 carbon steel in the different water samples and control samples. In contrast with control samples, the corrosion rate of N80 carbon steel decreased 41%, 23%, 18% and 4% in the presence of HPOA, HPOB, WHPO and HPI, respectively. The results were further confirmed by the EIS test. In the presence of the four fractions (especially HPOA), the radius of the semicircle in the Nyquist plot was much larger than that for the control samples, which indicated that the impedance in the EIS test of the HPOA sample was much higher than that of the control sample. The dissolved organic matter (DOM) could adsorb onto the surface of the electrode and form a protective film, which could inhibit electron transfer and increase the electrochemical impedance of the electrochemical test system.