The presence of free metal particles is one of the important factors that restrict the stable operation of DC gas insulated metal enclosed transmission line（GIL）. Electrode coating can effectively reduce the activity of particles and improve the degree of system insulation. We studied the effect of electrode coating on the charge and moving activity of the metal particle under DC voltage with different polarity

and established a platform for metal particle charge measurement and motion observation. Moreover

we proposed an "active index" M of metal particle

and analyzed the active level of the particle in different coating conditions. The experimental results demonstrate the existence of time-delay characteristics for the particle under electrode coating

and the time delay under the negative polarity is 16% higher than that of the

positive polarity. After the lower plate is coated

the particle is charged by conduction and micro-discharge when it is stationary

while it is charged by the micro-discharge when colliding with the dielectric film. The lifting voltage of the particle can be increased by about 10% after the electrode coating

and the "active index" M of the particle movement will be reduced by 69%

9

4%. It is concluded that the ground electrode coating should be utilized under the positive voltage; while the double electrodes coating should be adopted under the negative voltage.