In order to study the external form characteristics of pantograph-catenary arc during the process of rising pantograph

the images of the pantograph-catenary arc are collected based on the pantograph-catenary arc test device and high-speed COMS（complementary metal oxide semiconductor）camera. The movement mechanism of the process when arc burn is analyzed and the digital image process technology is used for image enhancement

edge detection and gray contour plotting. And the arc area is calculated

the influence of current on the area of arc is analyzed. The results show that static pantograph-catenary arc generally experiences five phases:triggering-diffusion-stable combustion-diffusion-extinction

and arc profile is elliptical; the image enhancement

edge detection and gray contour plotting realize the display of the energy emission range

the accurate local the feature extraction and the description of temperature gradient and plasma density gradient for pantograph-catenary arc. The arc area increases with the traction current increasing significantly

but not in direct proportion to the square of traction current. The time that arc achieves to the steady burning state gets shorter as the traction current gets larger. The conclusions above provide a theoretical basis for further researches on the external form characteristics and internal plasma parameters of pantograph-catenary arc in high-speed train.