Abstrct: As so far, because of the existence of rust complicates the electrochemical corrosion process, it is difficult to accurately measure corrosion rate of carbon steel by traditional electrochemical methods. In this paper, weight-loss method and different electrochemical tests such as polarization curves (PC), electrochemical impedance spectra (EIS) and linear polarization resistance (LPR) were used to study the corrosion behavior of the Q235 carbon steel immersed in seawater for 1 year. The results show that both the electrochemical and weight-loss measurement estimations have the same degressive trends during a short immersion period (for about 8 weeks), while the electrochemical measurement result turns to increase after 8 weeks’ immersion in seawater. The longer the immersion time, the bigger the deviation. The experiment indicated that the rusts deposited on the electrodes had a great influence on the corrosion behavior. The constituents of the corrosion products formed on the rust and base steels were characterized by XRD respectively. There is an obvious increasing of β-FeOOH in the corrosion product accumulated on the carbon steel with the immersing time going, and the reductive reaction of β-FeOOH during the electrochemical test progress leads an overestimate of the corrosion rate, which caused the deviation between weight loss method and electrochemical tests. In order to solve this problem, a -25μA?cm-2 cathodic galvanostatic polarization was done to counteract the reduction current during the electrochemical test progress. After the pre-polarization, the electrochemical measurement results coincided well with weight loss, which means this pre-polarization showed a good calibration of the deviation between the two measurement methods.