Selection and evaluation of protective coatings is an important part of heritage conservation. Compared with the traditional accelerated corrosion aging test method, electrochemical impedance spectroscopy (EIS) is qualitative, faster and more accurate, and can be directly used as a non-destructive method for studying cultural relics. This paper introduces the theory, experimental and analytical method of EIS and summarizes its application on metal relics, including bronze, iron and silver objects. The EIS method can be used to select and evaluate protective coatings.