The work aims to investigate the influence of Pseudomonas sp. on the degradation of polyurethane varnish coating in marine environment. Polyurethane varnish coating samples were immersed in the sterile seawater and Pseudomonas sp. inoculated seawater respectively. Electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) were applied to evaluate the anti-corrosion property of coating, observe surface morphology and represent molecular construction of samples immersed in different environment. The capacitive loop diameters of Nyquist plots and low-frequency impedance of Bode plots for samples immersed in sterile seawater and Pseudomonas sp. in-oculated seawater decreased at 1 h~35 d, and the decrease of these data of Nyquist plot and Bode plot in Pseudomonas sp. inoc-ulated seawater was significantly larger than that in sterile seawater during the immersion. The equivalent electrical circuit (EEC) model for sterile seawater system had only one time constant at 1~48 h, and then two time constants at 5~35 d. In Pseudomonas sp. inoculated seawater, EEC model had only one time constant at 1~48 h, two time constants at 5~29 d, and then three time constants at 35 d. Coating resistance of samples was 8.23×107 Ω?cm2 in sterile seawater and 5.14×107 Ω?cm2 in Pseudomonas sp. inoculated seawater for 36 h. Coating resistance was 5.61×106 Ω?cm2 in sterile seawater and 7.03×105 in Pseudomonas sp. inoculated seawater for 35 d of immersion. Reduction of coating resistance of samples immersed in Pseudomonas sp. inoculated seawater was obviously larger than that in sterile seawater at 36 h~35 d. From SEM results, after 30 days of immersion, the surface of samples in sterile seawater was smooth and intact, but a layer of biofilm composed by cells and metabolite formed on samples surface immersed in Pseudomonas sp. inoculated seawater, and a plenty of pits and powdering traces were also found. From the results of FTIR, the content of C—O in the ether group and N—H of samples immersed in seawater inoculated with Pseudomonas sp. were significantly lower than that of samples immersed in sterile seawater. Through the electrochemical results, Pseudomonas sp. can significantly reduce the corrosion resistance of coating, and result in the degradation of coating. Results of SEM and FTIR prove that Pseudomonas sp. can damage the C—O in the ether group and N—H of polyurethane molecular, and then cause the degradation of coating.