Abstract: The closing inrush current generated by the photovoltaic power station will find its second harmonic ratio increased after it is transformed by the current transformer（CT）.And when an internal fault occurs simultaneously within the area,the short-circuit current of the photovoltaic inverter will also bring an extra high content of second harmonic,which will make the differential protection of the main photovoltaic power station unable to remove faults timely during the inrush current blocking.According to the phase difference characteristics of fundamental wave and second harmonic of the differential current of the main transformer,a working mode of preventing protection maloperation to identify the fault occurrence time in the inrush current blocking process and increase the fault setting value timely to avoid protection locking based on differences of the second harmonic ratio when the inrush current and faults occur within the area. The PSCAD/EMTDC software is used to verify the second harmonic ratio change and protection action after the fault setting value is selected.The results show that the proposed differential protection working mode of the main transformer of the photovoltaic power station has excellent performance and can reliably remove the internal faults when the inrush current occurs.