Compared with traditional measurement methods such as current and voltage, the image of the partial arc on ice surface captured by schlieren technology is more intuitive. Its image processing and refractive index field reconstruction are the basis for quantitative analysis of physical characteristics such as geometric size, density and particle distribution of discharge. Based on the optical deflection characteristics of the discharge channel, the principle of measuring the discharge channel by schlieren imaging technology is introduced. A set of image processing and refractive index field numerical reconstruction method for the discharge channel on the icing surface is proposed. The accuracy of the method is verified by numerical experiments. The results show that the designed schlieren system has a spatial resolution of 10 ~ 100 μm / pixel and a temporal resolution 1 ~ 38.45 μs. The proposed refractive index field reconstruction method has high accuracy and can effectively obtain the refractive index field in each discharge stage of ice partial arc formation.