Abstract: The reliability of cathodic protection(CP) on carbon steel buried in sea mud containing SRB was evaluated with emphasis on electrochemical impedance spectra(EIS) under different CP potentials.The relationship among CP potential,corrosion rate and bacteria activities was summarized based on EIS results,weight-loss test and number-calculation of bacteria with MPN method,which showed that the steel under potential of-950 mV(CSE) was relatively well protected with a stable and low corrosion rate.The growth activities and stability of SRB were low under higher CP potential.-950 mV or even lower potential was needed to ensure effective protection.