When the photovoltaic power supply is connected to the distribution network, if it is damaged by arc flashover, it will lead to major equipment faults. Therefore, the fault classification and diagnosis method of photovoltaic power supply connected to the distribution network under the analysis of arc flashover is proposed. Using the superposition lightning flashover model based on the principle of mathematical statistics, obtains the arc flashover changes of equipment when lightning strikes, analyzes the physical quantities related to arc flashover hazards according to the arc flashover characteristics of these equipment, and calculates the harmfulness of various parameters of arc flashover through ieee1584 algorithm, Input the calculation results into the deep cycle Q network model for classification training, and obtain the fault classification and diagnosis results of photovoltaic power supply connected to distribution network equipment. The experimental results show that this method can realize high-precision fault classification and diagnosis of multiple fault types and different modes.