In order to discuss the corrosion mechanism of tin film, and prevent the efflorescence and fragments falling off Tin-coated pottery, microphotography, X-ray fluorescence and X-ray diffraction methods were used to analyze the tin. The film contained β-tin, α-tin, stannic oxide and stannous oxide. The corrosion mechanism of the tin film is discussed in combination with the test results. It was found that β-tin irreversibly turns into α-tin, with a lower density, below 13.2 ℃ and thus the volume expansion is the major cause of tin corrosion. Methods for the reinforcement and pasting back of tin film were selected and the treatment effect on two Tin-coated objects was good. In addition, according to the characteristics of Tin-coated pottery, some suggestions on preservation environment are also put forward in the paper.