The impact of the energetic plasma produced by corona discharge in air will lead to breakage of C—C bonds in the main chain of polymer

and gradually lose their insulation properties. Kapton-type polyimide film are widely used in gas-solid insulation of DC UHV power equipment

and the corona effect will directly affect the security and stability of equipment and even UHV power system. Consequently

we investigated the chemical reactions of polyimide in DC corona discharge plasma（O

3

–

HO–

H

3

O+

NO+ and positive/negative polar ions）

respectively

in similar conditions to explain the degradation mechanism. The ReaxFF reactive force field molecular dynamics method was applied to simulate the de

composition of Kapton under the influence of DC corona discharge. The simulation results indicate that transfer energy will occur when the Kapton contacts with impact plasma ions

followed by chemical reactions with plasma and dissociated active free radicals

resulting in polyimide backbone cleavage. Thus

the gaseous small molecules（mainly in carbon monoxide and water vapor） are released. It is confirmed that the positive DC corona is more obvious to the polyimide by the polarity corona effect simulation

which is consistent with the experimental results. As the simulations above demonstrate

ReaxFF can provide an effective micro mechanism for clarifying the effect of polyimide insulation failure caused by discharge.