Abstract: This paper introduces the test theory, experiment method and test equipment of Electrochemistry Impedance Spectrum (EIS) technique in the evaluation of pipeline coating. The equivalent circuit model for metal-coating-fluids system is established combined with actual coating system of pipeline. The authors use EIS to analyze the actual coating of pipeline system, adopt the nonlinear least square method to optimize EIS data, apply VC to develop the program to realize the arithmetic and draw up impedance figures by ORIGIN software. The analytical results show that among the coatings the salt water resistance osmosis of No. 2 coating system is poor and anticorrosion performance of No. 3 coating system is good.