In order to explore the damage mechanism of PI/Al

2

O

3

film caused by corona discharge（CD）

scanning electron microscopy（SEM）

energy dispersive spectroscopy（EDS）

and infrared spectrometer（FTIR） were used to study the PI/Al

2

O

3

film in entire corona aging process based on the standard GB/T 22689—2008. The results show that the surface of the corona damaged zone was destroyed seriously with the time of CD increasing

and the content of organic matter was decreasing gradually with more and more Al

2

O

3

appeared and formed a continuous Al

2

O

3

layer on the surface. Circular hole of about 20 μm was formed after breakdown of the corona aging. By locating the breakdown point

we found that the position of breakdown point was in the central

zone which hardly dissipate heat insteading of in the corona damaged zone. These results indicate that the corona aging breakdown of composite film is not a traditional electric breakdown or electrochemical breakdown but a thermal breakdown due to a lot of heat generated during CD process.