Objective To investigate the corrosion behavior change of carbon steel with immersion time in the interference of stray current and cathodic protection (CP). Methods In this paper, man-made small damage points were made on carbon steel pipe which was coated. The electrochemical impedance spectra (EIS) of the Q235 carbon steel with the damaged coating were studied, which were affected by the DC stray current interference, the cathodic protection and the combined action of DC stray and CP over time. The analysis was conducted according to spectral information and spectral data fitting. Results All the low-frequency impedance in Bode diagrams and capacitive reactance arc radius of Nyquist diagrams of EIS spectra under any conditions were gradually increasing over time. Through the spectra and data fitting, it was found that the larger the stray current was, the more serious the corrosion was; when the immersing time reached 15 days, the polarization resistance under the condition of stray current of 20 mA was four times as much as that under the condition of stray current of 200 mA. Cathodic protection had a protective effect on the stray current corrosion. Comparing the conditions of -1000 mV (CSE) and -850 mV (CSE), the polarization resistances under the condition of -1000 mV were higher all the time. Within a certain limits, the more negative the cathodic potential was, the greater the polarization resistance was, and the better protection effect was obtained. Conclusion Within a certain limits, no matter stray current or cathodic protection is applied alone or together, it is always found that with smaller stray current and more negative cathodic protection potential, the protective effect for carbon steel is better and the corrosion degree is less. It is feasible to monitor the corrosion of pipeline by EIS technique.