The internal and external corrosion protection of oil and gas pipelines mainly depends on highly corrosion-resistant coatings. However, it remains a challenge to assess the protective performance of existing coatings non-destructively. In this work, a double-electrode electrochemical impedance probe was designed to estimate the degradation of coatings. The lab tests show that the EIS measured by the double-electrode probe agrees well with that by conventional three-electrode cells. In addition, the |Z|_{0.01 Hz} increases first and then becomes stable with the increasing distance between the two electrodes. Through the simulation of COMSOL electrostatic field, it shows that the coating impedance measured by the double-electrode probe is twice that by a single-electrode probe. Although, the coating degradation state can be revealed using either probe, but the use of double-electrode probe can avoid the troubles of requiring to find out the iron-related leaking spot emerged on the coating during field tests. Eventually, a portable impedance meter for in situ non-destructive monitoring of coating is designed based on the double-electrode probe. Through online evaluation of coating degradation state, the impedance meter may provide guidance for the determination of preventive maintenance cycle and maintenance area of degraded coatings for pipeline or large tank.