Abstract: The visible digital image of corona discharge contains rich chromaticity information,in this paper,the chromaticity index of digital image processing technology was used to study the corona discharge in air.Firstly,the true color image of discharge was transformed into three primary color components,then the chroma gray value of the discharge region of R,G and B components was extracted and the proportion of chroma component gray value was also calculated.It is found that the discharge voltage increases,the gray value of true color image and three chroma components increases,which can reflect the change of discharge intensity.Compared to the traditional pulse current measurement,the result is better.When the discharge intensity is weak,the proportion of G component is the largest,the proportion of B component is in the middle,and the proportion of R component is the smallest.When the discharge intensity is strong,the proportion of B component is the largest,the proportion of R component is in the middle,and the proportion of G component is the smallest.Changes in component proportion can be used to determine the severity of the discharge.The results of spectral measurement support the above analysis results.On this basis,the chromaticity division method of the discharge stage is presented,which is characterized by the difference of the component proportion.