Photovoltaic power generation is intermittent and fluctuating due to external environmental factors. It will cause the current part of the line protection malfunction and failure to trip and sensitivity decrease when distributed PV system connected to distribution network. Model identification pilot protection principle is improved and optimized based on fault feature of analyzing distributed PV connected to distribution network. Thus the PV connected to the distribution network protection criterion is proposed. In the improved model identification pilot protection method, both the external zone fault and internal zone fault are equivalent to different inductor circuit models; and internal and external faults can be distinguished based on the error values of internal and external model when line is fault. PSACD/EMTDC simulation verifies that the method effectively overcomes the influence of branch current of photovoltaic accessing to distribution network, and can quickly cut off the fault, which validates the correctness and effectiveness of the model identification pilot protection principle used in photovoltaic grid connected.